As a general rule, this is how I make my selection:
Layer3 v. Layer2
3xxx v. 2xxx
Stackable v. non-stackable
3750 2950 2975 v. 2960 3560
*** there is a 2960-S which is apparently stackable. Never seen one.
And then, 24 v. 48 ports
And, number of SFP ports required, 10Gb ports required, power redundancy.
It's good to talk to a good sales rep - one who knows what s/he's talking about(!).
They'll try to make a happy customer of you and reduce the risk of you getting the wrong thing.
Plus s/he might throw a bit of freebie merchandise your way if you're lucky...