Pippins review is an excellent analysis of the practical in your face issues experienced with these plugins.

Another aspect would be to look at the code vomit spewed forth by pretty much all of them. Some of them have horrendous complex PHP, which makes it nigh on impossible to work out how to extend them or work around them, and others include gob smacks of CSS and JS which look like nothing more than code diarrhea.

And another aspect would be to look at what features they offer.