this has been asked a thousand times throughout dozens of phones... only one answer:
Try it out and see for yourself. Each one is different, so how is one better than the next? One rom might be less stable than another but could be due to hardware revisions in your phone etc...
HARDSPL / USPL - check out the USPL thread for an explanation of the differences. Again, it's entirely up to you. This is the information that I've searched and spent 5 minutes reading for you...
Hard SPL - more reliable, void warranty, flashing a permanent SPL
USPL - less reliable, no void, temporary