[T-Mobile Samsung Galaxy S II SGH-T989] aranurea:
So, I did lots of research and reading and all sorts of information gathering. I have reached the conclusion that the HTC One S is better than T-Mobile Galaxy S II, but not by a large margin. Now, this is just my opinion, but it is based off of lots of information digging and research. I will try to be as unbiased as possible, leaving usage out of the equation. I do not own the One S and will try to ignore any experience with the GSII.

Now, the core of both phones are very much the same both having Qualcomm Snapdragon processors, but the One S has the the edge in this one as it has the newer version, the Qualcomm Snapdragon (S4) Krait. The Krait can fetch, decode and execute more instructions in parallel than its predecessor (Scorpion, Snapdragon S1/S2/S3). I believe the S II holds the S3 (tell me if I'm wrong). This is not a minor difference and is a very evident difference. They both have 1 GB of RAM.

Now, the screens are preferred by different people because they are so different. The S II has a 480x800 Super AMOLED Plus screen at a size of 4.5in. measured diagonally. The One S has a 540x960 Super AMOLED screen at a size of 4.3in. measured diagonally. The issues on the Galaxy S II's screen are only the lines and blotches (aka the mura effect) as far as my research got me. Now, the One S doesn't have that problem (again, all based on research), but it does have problems such as unusual coloring around text,images, and icons. This is due to the phone using alternating red and blue/green and red pixels rather than the traditional Red, Green and Blue (RGB) pixel arrangement. Another issue with the screen is contrast shift. Look at the screen from anywhere off dead center and a distinct blue hue will descend, which is very noticeable. Finally, while the bright, vivid colors are nice to look at, the AMOLED screen tends to over saturate colors meaning the color temperatures are completely off a lot of the time, leading to inaccurate and off-looking images. These screens have major differences but both are preferred by different people. For example, I like the S II screen compared to the higher res screen of the Sensation, due to the color advantage, where as my brother is the opposite.

Both phones come with 16 GB internal storage. The S II user gets to utilize 11 GB of it and the One S user gets to utilize 10 GB with 2 GB for app. The big difference is that the S II has expandable external memory up to 32 GB whereas the One S has no external storage slot. This is a deal-breaker for many, but light to moderate users can live with it.

The cameras are the same except that the One S has a still shot feature while recording a video, but this requires a 4:3 aspect ratio while recording to utilize the 8 megapixels to take the still shot, rather than the preferred 16:9. (Many users are reporting that the One S camera although it has the same number of megapixels, takes better pictures and is a much better camera overall).

The S II boasts a 1850 mAh battery where the One S has a 1650 mAh battery. The One S has, on average, 20-24 hours of life on a single charge. BEWARE: THE BATTERY ON THE One S IS NOT REMOVABLE! While still annoyingly low, it is on a par with most smartphones these days. The Galaxy S II also has very similar battery life even though it has more mAh. This is due to the larger screen mostly.

Software is something that will not be discussed in detail because of bloatware and the fact that the software in Android phones is very malleable.

The One S ships with Android 4.0 (Ice Cream Sandwich) and Sense 4.0. The Galaxy S II ships with Android 2.3.5(Gingerbread) which is upgradable to Android 2.3.6(Gingerbread) and is yet to receive an official Android 4.0 update. The Galaxy S II also comes with TouchWiz 4.0. The Android 4.0 on the One S works extremely well with its upgraded processor and is very smooth. The Galaxy S II's Gingerbread also runs very smooth on its own processor. Both phones can be rooted and different ROMs can be flashed on both.

This is it so far. I will be adding any new updates in the same format as devs do.