I often see people mention how Android doesn't have SmartGo as iOS does.
Well I've tried a bunch of Go software on Android (some for a few bucks some free) and in my opinion there is a good replacement: GoGrinder. It allows to include custom problem collections too, and while there isn't the cool SmartGo zoom function I find it's pretty sufficient and the stone/board graphics are nice too. If you've got an opinion to share please do ^^.

In general I use on Android: KGS (duh), GoGrinder (for problem-solving), gobandroid (for looking through SGFs I downloaded), Igo Clock (for turning my phone into a clock when playing in a cafe).
I recommend board skin 'lironah' and stone skin 'sente' for gobandroid .

Also, in case there are problems with importing certain combo-SGFs such as the Gokyo Sumyo collection into GoGrinder (one SGF containing multiple problems): GoGrinder will pop up warnings about this. Apparently http://www.linux-support.com/cms/en/com ... -vari-man1 should be able to split SGFs but I haven't given it a try yet.