I like SSL more then Bad Eggs. They are very similar and neither are horrible. Bad Eggs just gives the advantage to the person that went first. That really bugs me. The good thing about Bad Eggs is that leveling up doesn't give you a totally unfair advantage over another person. Overall though SSL is more enjoyable for me.
Bad eggs is basically a shell shock with worse graphics. It doesnt lag near as bad on bad computers. Shell shock has better overall gameplay, though. The aiming for bad eggs is a lot less precise. Both of them had one thing I hated, and that was that if you paid, you would get better weapons that are unfair.