The title is self explanatory I think.

On my Imperial, I left in a full set of Imperial Steel. Didn't know a set of normal steel was that much better, just really like the dragon motif's on the Imperial Steel set.

I have a character still in riverwood with 100 smithing.

You must really like working at the lumber mill then.

i visit Riverwood a-la 1ce a week... last time i left Riverwood i was wearing Deathbrand armor

My first character, a warrior/thief, skipped Riverwood completely, eventually found the dragon claw by exploring, and when he finally did step into Riverwood he was wearing leather armor. My second character who is a mage camped out for a day and night at a small bandit camp after escaping Helgen, then walked into, stayed for a few days, and left Riverwood with the same Novice Mage Robes from Helgen's prison.

My first character left Riverwood in a set of Imperial light armor.

I usually leave wearing Stormcloak or leather. Heavy armour svcks IMO, I prefer agility.

First characters? Novice Robes. But nowadays I like to find a nice civilian outfit in Alvor's / Gerdur's house. And hide bracers; always hide bracers! (ooooooh, 200 points, btw.)

My characters have always left Riverwood for the first time and for the last time in the same outfit: Thalmor uniform.

how do you get thalmor robes at the start?

None I just had clothes on.