Blizzard unitframes are, in my opinion, very bad, so I always change them first. I use X-Perl; they look good and you can easily customize them as you want.
When that fixed, I'd get SCT addon and FuBar. I like watching things like my mp5 regen, pet dmg and heals, and I dont like "Blizzards way" to show that. FuBar lets you use a FuAddon that shows experience, location and what I need of options for other addons.
On some chars, I get Bartender3 addon to get new actionbar layouts, but mostly I use Blizzard bars.
My UI.
You could try download WowAceDownloader. It shows alot of Ace addons in a list and you can just pick what you want and extremely easy install them.