A fairly new entry onto the iOS media-player scene is iMPlayer 1.3.0 ($2.99). While the player has some useful features — which I will elaborate on — in a word: I do not recommend this player, unless you need its bookmarks feature. Otherwise, its performance is just too weak for its price point.
The advantage of the player is its ability to add bookmarks anywhere, in any kind of a video, along with a small framegrab. Unfortunately, very few other players are capable of doing this. I've attached a link to an example using the standard Monsters MKV test video.
Incidentally, the screenshot above shows there's no Retina support when software decoding is used; hence the low resolution. Also, pay special attention to the errors the weak H.264 decoder of the app is introducing to the decoded frame. For example, to the left of the green creature on the left, you can see rectangle-shaped green blotches — they have been introduced by the decoder. (The second thumbnail at the bottom also shows such problems.) Should you want to manually back up (or migrate to another iDevice) your bookmarks, they're under Library/BookmarkDir, directly accessible via, say, iExplorer.

The screenshot above shows the Monsters thumbnails.
Pros
- Excellent, unique bookmark support
- iOS-native files are played back in hardware (and with Retina-friendly resolution)
- Apple CC tracks displayed in iOS-native files
- Good WMV support (also WMA Pro) – albeit not as fast as that of, say, the, generally, excellent AVPlayerHD
- Tolerable DVB TS support if you don't need subs/multiple audio tracks (scrubbing and aspect ratio changes supported; however, merging the interlaced frames is very ugly when there's plenty of movement on screen. There's no subtitle rendering or audio track changing.)
Cons
- Software-decoded videos are played back in low-res on Retina screens Non-Universal, which is further made worse by the high price ;
- No AC3 ;
- No DTS ;
- No streaming support;
- No support for audio-only files (WMA, FLAC, APE, WAV, WV, OGA stb);
- Very slow H.264 decoder ;
- No MKV hardware playback;
- No SSA subtitle support ;
- No textual subtitle support in MKV files (see Monsters);
- No gesture-based ffwd/rewinding ;
- No playlists (however, you can still create folders in the app) .

