Woo! Number 9 is great
I'd recommend their first album but there is approximately a 900.3 (Recurring of course) % chance that Mig will recommend that album when he sees you talking about T-ara and then say it's better than anything else they've done by far
Which I disagree with, their first album is awesome though but they have lots of great stuff just as good like number 9.
Their older stuff has a more retro disco vibe to it than their newer stuff though, that was their original concept although they seem to have largely dropped that now, try some of it though:
https://www.youtube.com/watch?v=6-HG2Z6M4ww
https://www.youtube.com/watch?v=QgGpcQBFacM (<-- a very fun MV)
https://www.youtube.com/watch?v=vSOgvfGTHlg (a collab with supernova)
Also I forget if you like the same kind of MVs as me? the very dramatic MVs with a story line?
If so, T-ara are the queen of them and when they do them, which is often, they really go big.
Here is the drama MVs for Day By Day and Sexy love combined into one since day by day was a to be continued and sexy love continued it
https://www.youtube.com/watch?v=O9dk_18FfmY