Lol at this thread, one post by NO_WALKING and the rest is all damage control from there.
To OP: You'll have to focus your flavor...
If you want more focus on summons, I would go Sorcerer.
If you want more focus on stealth, I would go Nightblade.
And if summons are what you are interested there are a couple non-sorcerer paths...
Nightblade, as stated has some kind of summon shade.
Also Dunmer have a summon ancestral guardian,
And I wouldn't be surprised if the Wood Elves got some kind of naturey style summon, like in Skyrim.
I think that if Deadra Summoning is really important though I would go for the Sorcerer Class. You should be able to pick and choose enough other things to *help* out with stealth, and the additional companions would certainly be of service.
Stats level up naturally at an even rate for all classes. Additionally at every level-up you get to distrubte a point to either Health, Stam, or Magic. Class choice has no bearing on this. So you will get better at all those things, but specialize however you please.
But yes just active and passive abilities are the only defining aspects of class. (At least that have been released so far...)