While bigger is generally better.. you fish limits will be more based on length rather than height or width. It's a pain getting into the 90 I have now. Reaching the back corners is a .. well... wet experience..
If you're going 4, I'd do the 90.
Soo.. your decisions are this:
a) Filtration: Sump/wetdry, canister, HOB
(hang on back) or some combination of
d) Sand/Crushed Coral - Sand is much better...
e) Live Rock ?
f) If you decide on sump or wetdry .. drilled or overflow..
Those are some of the decisions you will need to make