Apple is expected to unveil the much-anticipated next-generation iPhone on Tuesday at its Cupertino headquarters, where the technology giant is conducting an event titled Let's Talk iPhone.

The so-called iPhone 5 would be running on Apple's latest mobile operating system iOS 5 and would support iCloud that allows wireless storage of music and other content.

But, this time it would not be an easy task for Apple to hit the bull's eye right away as there many Android smartphones with killer features and specifications that may give consumers an alternative to iPhone 5.

Let's take a look at the top five iPhone 5 contenders:

Google Nexus Prime

Speculations are rife that Samsung and Google are readying a killer device under the name Nexus Prime, which could give iPhone 5 a run for its money in terms of both OS as well as specifications.

Nexus Prime is expected to run Android Ice Cream Sandwich and feature a Super AMOLED HD display with 720p resolution. Prime's display will include a 4.5-inch panel with a PenTile layout, according to a report from BGR.

Nexus Prime will be powered by a TI OMAP4460 chipset clocking at 1.5GHz. The report added that Nexus Prime won't feature physical Android menu buttons below the screen anymore as everything will be software-based.

The camera will be 5 megapixels, but the sensor is expected to be improved for high quality images and better low-light conditions. Like many Android handsets on the market, the Nexus Prime will offer a front-facing 1-megapxiel camera for video chat.

The 5-megapixel camera, however, is said to sport an advanced sensor delivering top image quality in addition to superior low-light performance. Moreover, the device would have 4G LTE support and at least 1GB of RAM, the report added.

Google is said to be aiming to launch the device around Thanksgiving.

Samsung Galaxy S2

Samsung Galaxy S2 is touted as iPhone killer. The phone runs on the 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. The phone comes in 16GB/32GB internal memory configurations with 1GB RAM.

Galaxy S2 comes in three variant through AT&T, T-Mobile and Sprint, whose version is called Samsung Galaxy S2 Epic 4G Touch.

Samsung recently showcased its Samsung Galaxy S2 LTE phone at IFA Germany. The Galaxy S2 LTE is a larger cousin of Galaxy S2 both in terms of size and hardware specifications.

The Galaxy S2 LTE sports a 4.5-inch Super AMOLED Plus display with 800x480 screen resolution. It is powered by a 1.5GHz dual-core processor and offers 16GB internal memory.  The phone is 0.37-inch thick and weighs 4.6oz. Galaxy S2 LTE will also feature an 8MP rear-facing and 2MP front-facing cameras. It is fitted with a Li-on 1850 mAh battery. The phone will come pre-loaded with Android Gingerbread.

Motorola Droid Bionic

Motorola released its Droid Bionic smartphone on Verizon's network on Sept. 8. The device runs the Android Gingerbread 2.3.4 OS and is powered by dual-core 1 GHz processors, 1 GB of RAM and a stunning 4.3-inch qHD display, with a resolution of 960x540-pixels.

The Droid Bionic sports an 8 megapixel auto-focus camera with flash and 1080p HD video capture, as well as a front-facing camera for video chat over 4G LTE, 3G or Wi-Fi. The phone has 16GB of internal storage and a pre-installed 16GB MicroSD card, which can be expanded to 32GB.

Verizon offers the Droid Bionic at $299 with 2-year contract.

HTC Vigor

HTC is said to launch another Android Gingerbread smartphone in the name of HTC Vigor. The smartphone, which is rumored as a successor to HTC Thunderbolt, is expected to have a 4.3-inch display with 1280x720 screen resolution, 1.5GHz dual-core processor, an 8MP camera.

HTC Vigor is also speculated to have 16GB internal storage and incorporate Beats Electronics Technology - best known for the high-performance line of headphones backed by hip-hop artist /producer Dr. Dre.

HTC Sensation 4G

T-Mobile launched the HTC Sensation 4G on its network in June. It is considered as one of the best phones on the market right now due to its cool aluminum design that embraces the sides, back, and even in the small portion of the Sensation's front.

HTC Sensation 4G, which comes with the 4.3-inch S-LCD capacitive touchscreen with the resolution of 960 x 540 pixels, has lived up to its name and has continued to receive rave reviews for its incredible performance in terms of nice screen, beautiful design, good camera and HTC Sense.

HTC Sensation 4G, which runs Android 2.3 Gingerbread OS with HTC's Sense 3.0 user interface, has a dimension of 126.1 x 65.4 x 11.3 mm and weighs at 148 grams. It is powered by 1.2 GHz dual-core Adreno 220 GPU Qualcomm MSM 8260 Snapdragon processor.

The phone also boasts an 8MP dual-LED flash camera with 1080p HD video recording capabilities, and a VGA front-facing shooter for video calling. The phone sports a 768 MB RAM and 1GB internal memory with support for microSD up to 32GB.

HTC's phone has T-Mobile's HSDPA 14.4 Mbps and HSUPA 5.76 Mbps support. It has Wi-Fi 802.11 b/g/n, DLNA, Wi-Fi hotspot support along with Bluetooth version 3.0 with A2DP and microUSB version 2. There is a Li-Ion 1520 mAh battery found in Sensation 4G which can give up to 8 h 20 min of talk time.