Is it ok or better to upgrade a late 2011 MBP 13" 2.4 GhZ intel Core i5, 4 GB ram 1333 MhZ DDR3, intel HD graphics 3000 384 MB to mountain lion up from lion or will it be slower and give worse results? THANK YOU!!!!!!!! 
Do a fresh install.
I upgraded from Lion (no clean install yet) and have zero issues. Even VMware Fusion continued to work just fine.
ML is faster/better than Lion in all respects save for battery life. IMHO the battery life trade-off is worth it for the speed increase. Coming from Lion, the improvement is noticeable.
But for the laptop specs I stated is it ok? Yours is better than mine.