Samsung is facing substantial competition from other Android smartphone makers. Its long-awaited flagship Galaxy S2 will soon arrive in the United States, but some contenders will try their best to spoil the party.

The top five Galaxy S2 contenders are: Google Nexus Prime, Motorola Droid Bionic, Motorola Photon 4G, HTC Holiday, and HTC Vigor.

Galaxy S 2 was announced at the Mobile World Congress in Barcelona in February and since then the phone has continued its march. Galaxy S2 comes to the U.S. after selling a record 5 million units in 85 days in Europe and Asia and is the best-selling Samsung phone ever.

In the U.S., Galaxy S2 would be carried by AT&T, T-Mobile and Sprint, whose version would be called Samsung Epic 4G Touch. Galaxy S2 is expected to come to Sprint's network on Sept. 16 and would be launched on AT&T from Sept. 18.

Galaxy S2, which runs on Android 2.3 Gingerbread OS and sports Samsung's TouchWiz UI, comes with an 8-megapixel camera with flash and can record HD video in 1080p offering the richest video content on a smartphone. The phone also has the front-facing 2-megapixel camera for video chat.

Samsung Epic 4G Touch on Sprint comes with a 129.5 x 68.6 x 9.6 mm dimension and weighs 129 g, while the T-Mobile version, fondly known as Hercules, has 131 x 70 x 9 mm dimension. As the AT&T version retains 4.3-inch display, it is expected to feature 125.3 x 66.1 x 8.5 mm and weighs 116 g.

T-Mobile and Epic Touch 4G version of Sprint has 4.52-inch display screen whereas AT&T version retains 4.3-inch screen of original Galaxy S2 version sold worldwide. It is powered by a dual-core 1.2 GHz ARM Cortex-A9 Mali-400MP GPU Orion chipset. The phone comes in 16/32GB internal memory configuration with 1GB RAM.

But, does Samsung Galaxy S2 has enough firepower to challenge the top 5 new 'super' smartphones that run on Google Inc.'s Android?

Google Nexus Prime

The Nexus Prime will most likely be the first smartphone to run on Android 4.0 Ice Cream Sandwich and will likely be launched in October, according to the Korean-language Web site Electronic Times. Ice Cream Sandwich will combine the best features of Honeycomb (Android tablet OS) and Gingerbread (Android smartphone OS).

The Google Nexus Prime has been called an absolute beast among smartphones and there is a very good reason. The smartphone will boast a dual-core Snapdragon processor that will include Krait chips from Qualcomm, and a 1GB RAM.

It is not yet known if the processor will be of either 1.2GHz or 1.5GHz. The Krait-based Snapdragon processor will have the ability to run at a lightning speed of 2.5 GHz per core at the least, which will make it more than 100 times faster than a normal ARM-based CPU.

Tech Web site BGR had offered an exclusive sneak peek into the features of the next Nexus model, which was called Nexus 4G. According to BGR, it was an absolute beast and would feature a next-generation dual-core 1.2GHz or 1.5GHz CPU as well as an OMAP 4460 or a, ultra low-power 28nm Krait-based Snapdragon.

The report had said the Nexus phone will feature a 720p HD “monster-sized display, a 4G LTE radio, 1GB of RAM, 1080p HD video capture and playback, a 1-megapixel front-facing camera, and a 5-megapixel rear camera.

Britain's Telegraph reported that the Nexus Prime is reportedly being built by Samsung and that it may sport a 1.5GHz dual-core processor as against the single core, 1GHz processor in the Nexus S. The display will be upgraded to a 4.5-inch 720p Super AMOLED HD screen, whereas the Nexus S display is 4-inch and with lower resolution, the report said. The industry rumors suggests that the Nexus Prime will be unveiled in October.

Motorola Droid Bionic

Motorola’s Droid Bionic is another smartphone with its 4G powered LTE support that is sure to make waves on its release. The launch of the Motorola Droid Bionic is finally drawing near after several postponements and numerous leaks about the device.

Verizon Wireless confirmed on its Twitter page that the new beast of the Motorola Android phone will be unleashed on Sept. 8, as previously rumored by numerous sources.

No official specs have been confirmed yet for the Motorola Droid Bionic but after constant leaks there’s a widespread belief about what’s coming.

The Motorola Droid Bionic is powered by Android 2.3 and it looks similar to Droid X2, which is another dual core smartphone without 4G support. Droid Bionic has a huge battery power, and 4G LTE.

It is rumored to sport 4.3-inch or 4.5-inch qHD display with 960x540 pixels screen resolution. It is surmised that it will be powered by a Texas Instruments OMAP4430 1.2 GHz processor optimizing 1GB RAM. Droid Bionic is expected to feature Li-ion 1930 mAh battery and will feature an 8MP camera.

The Droid Bionic's expected specifications include Wi-Fi 802.11 b/g/n, DLNA, Wi-Fi hotspot (connects up to 8 devices and when on 3G connects up to 5 devices), Bluetooth version 2.1 with A2DP and EDR technology, microUSB version 2.0, touch-sensitive controls, multi-touch input method, accelerometer sensor for UI auto-rotate and proximity sensor for auto-turn-off.

Motorola Photon 4G

The Photon 4G is Sprint’s seventh Sprint ID-capable handset. The Sprint ID delivers number of applications, shortcuts, widgets, ringtones and wallpapers. The pack provides free-to-download stuff under its Everything Data plan, and users are allowed to download five packs at a time.

Motorola Photon 4G has 4.3-inch qHD capacitive touchscreen (960x540 pixel resolution), multi-touch input method, accelerometer sensor for UI auto-rotate, proximity sensor for auto turn-off, touch-sensitive controls, 16GB storage (up to 32GB with microSD support), 1GB RAM, 2GB ROM, WiFi, Bluetooth, 8-megapixel camera (with dual-LED flash, autofocus and geo-tagging features), secondary VGA camera for video chat, Android 2.3 OS (Gingerbread), 1 GHz NVIDIA Tegra 2 AP20H dual-core processor and HDMI port.

Moreover, the Photon 4G for Sprint is a world phone which means the consumers have international GSM roaming so that they can access their email, calendar and contacts from anywhere. As the phone includes enterprise-tailored security, it may attract corporate users. It also has Webtop application which was featured in Motorola Atrix 4G.

Motorola Photon 4G is priced at $199 on Sprint with a two-year contract, but Amazon Wireless offers the phone for $99.99 for new Sprint customers.

Reviews of the Photon 4G have been positive. Engadget gave the device a 8/10, saying it comes very close to dethroning Samsung's mighty Galaxy S2 as king of the Android hill. CNET UK gave the device a favorable review of 4.0/5 and described it as a Sprint iteration of the Atrix 4G because of similar specs.

HTC Holiday

The Holiday is rumored to boast a 4.5-inch display, supposedly the first of a new wave across the Android landscape with 4.5-inch displays.

The recent breed of Android phones found expression in 4.3-inch displays. The trend seems to highlight that the next barrage of Android phones will follow the 4.5-inch form factor. The arrival of such a piece from HTC is cause for concern for Samsung.

HTC Holiday is expected to have 1.2 GHz dual-core Qualcomm Snapdragon processor with 1GB RAM, Android 2.3 Gingerbread OS, 4.5-inch qHD display with 960x540 screen resolution, 8MP dual-LED flash rear-facing camera with 1080p video playback, 1.3MP camera for video chat, HSDPA up to 21 Mbps, HSUPA up to 5.76 Mbps, Wi-Fi 802.11 b/g/n DLNA support, advanced Bluetooth version 4.0 with A2DP and EDR, and microUSB version 2.0. The HTC Holiday is expected in early or mid-September with a price-tag of $199 to $249 at AT&T.

HTC Vigor

The phone from the HTC camp which is due to hit Verizon's 4G LTE network is rumored to sport a 1.5GHz dual-core processor. The phone, which is touted to be a replacement for the HTC Thunderbolt, is expected to don a 4.3-inch display with 1280x720 screen resolution.

Vigor is surmised to be fitted with an 8 MP camera. It will run on Android Gingerbread juice. Also it is expected to offer 1GB RAM, 16GB internal storage and is also surmised to incorporate Beats Electronics Technology - best known for the high-performance line of headphones backed by hip-hop artist /producer Dr. Dre. Leaked pictures of the phone were recently posted on Droid Life.