what would you say is the best city to sell and buy stuff and why

riften...lots of varied vendors and it only gets better as you get more and more of the speech perks and do the TG line. whiterun is a close second though...i especially like the drunken huntsman and elgrim's elixers since they never close!

Riften. If you are part of the thieves guild definitely do all you can in that quest line. It pays off if you aren't looking to put perk points into speach.

I tend to drift from town to town, after doing some creative alchemy, and bankrupt the potion and miscellaneous junk sellers. Except for that multilevel city in the east, I keep forgetting its name. I'm currently not very popular there.

Riverwood

Riften
Three general goods stores/stands
A jewellers
A smith
An alchemist
+
Once you complete the Thieves Guild
Three extra smiths
An extra alchemist

As others have said, Riften is very good, especially if you're in the Thieves Guild.

I don't mind Whiterun, either. General Goods, Alchemist, 2 blacksmiths, the hunting store and the jewelry stall.

Riften for sure.

Whiterun has 3 armorers with 1000+ gold (Eorlund and the two Warmaiden's merchants), 2 general goods merchants with 750 (I'm counting Drunken Huntsman here), and an Alchemist with 500+ gold. I don't count the stalls or the Bannered Mare because their merchant gold is fairly insignificant. Total = ~5,000 gold

Riften is a pretty close second. 1 Armor (1000+), 3 general goods store (750 each), a jeweler (750), and an alchemist (500) for 4,500 gold. If you're part of the TG, then it's Riften, no question.

If you're male and take Allure, then Solitude is kinda sorta your best bet, even though there is less overall merchant gold. 3 of the 5 major merchants are female, compared with 2/6 in WR, 2/6 in Riften, and 1/5 in WH.