I agree with Quantum about having hard times with branches in GoEye, however there are features not available in other apps. Go4Go integration, photo/graphics to sgf option, quite good options for sorting files, updates to actually running games(!) - pull to refresh option. The latter is very nice - It's possible to view games from Kgs on iOS via KGSArchives (games are there updated with every move). Ok that's all for now, maybe more later
[Later...]
These apps shouldn't be compared in versus mode. They have different set of features so direct comparison is always unfair in one or other way. Similar thing goes with EasyGo app. Very good app for different usage scenarios. Ok, in every app you can edit and review games and every mentioned app is great to do it, but very additional features makes each of these apps quite unique. EasyGo is best to study go problems and import games batches in zip, internal www browser also available inside the app, very good built in tsumego section. GoEye is great for viewing new international games from Go4Go or other go sites, and also for games from KGSArchives, pdf export. SmartGo Kifu - biggest offline database of games (GoGoD), players encyclopaedia, joseki/fuseki recognition, book view of sgf, ability to play against AI.
So each of these apps has it's own very good set of unique features.
In short - such comparisons should not be "vs" because these apps are complementary to each other.