They may look quite similar from a distance, but the HTC Titan and the Samsung Galaxy S II Skyrocket are two very different devices. The HTC device runs Windows Phone, while the Samsung runs Android. Check out the detailed comparison video which follows:
The Titan runs Windows Phone 7.5 (Mango) and features a 4.7-inch touchscreen display, 8 megapixel camera with 720p HD video recording with a 1.5GHz processor.
The Skyrocket runs Android 2.3 Gingerbread (Android 2.3.6) and features a 4.5-inch display, 8 megapixel camera with 1080p HD video recording with a 1.5GHz dual core processor.
source - PhoneDog