Southampton is miles ahead of Portsmouth in electrical/electronic engineering rankings. Both cities have good nightlife as far as I'm aware. The distance to campus depends on where you end up living at Southampton (don't know about Portsmouth). If you get an offer from both I'd go to Southampton.
I don't think Portsmouth do EEE but if you applied for MEng Electronic Engineering at both unis, the offers (according to the online uni sites) are:
Portsmouth: 300-340 UCAS points (equivalent to BBB-AAB)
Southampton: A*AA
This is quite a gap between the two unis - your decision should really reflect your capabilities. A good question to ask yourself is what are you aiming for, BBB-AAB or AAA+? As PQ said, you have 5 choices, a good idea is to pick one uni above your predicted grades, 3 that match your predictions, and one below (insurance). Good luck!
(I'm a Southampton EE student, feel free to ask questions)