i do not recommend plug and play as the name implies, you have very limited options if there are things you do not like..
i have a 24G and it does works if you are always on the ball doing water change and all.. do note that you can fit a tunze 9002 skimmer in there but it is still not sufficient IMHO..
Let me list the limitations of a plug and play system:
1. Almost everything is stock and would not be good enough..
2. to counter point 1, you need to modify.. plug and play systems leaves very little space for modification
3. Limited fishes and corals.. you need to get small fishes and small frags
4. weekly 10% water change and clearing of your wool fortnightly..
5. a small swing in parameter in a 3ft is a huge swing in a nano
that being said i had a great experience with my 24G and i managed to keep it well maintained till i went to NY for 6 wks and all went downhill.. still in the process of slowly restarting..
i wouldnt recommend nano for starters.. but somehow most people start with nano first dont they?