i gotta say of all Six Flags park i've been to Six Flags Over Texas was the best, it really was great fun when i was there. the last time i went was when Titan opened up. the park was clean, well maintained, and a lot of good rides.
from best to worst of the Six Flags parks i've been to.
Six Flags Over Texas (best one)
Six Flags Fiesta Texas (at a very close second)
Six Flags Great America (nothin against it, its a solid park, just liked the other two more)
Six Flags America (was a good park, but out by Superman and Batwing, it was very open, leaving a lot to be desired - then again the park has room to expand)
and
Six Flags Astroworld (was the little red-headed step-child of the Six Flags chain, most of the coasters were cookie-cutter and hand-me-downs- park was in bad shape up until its last year of operation, shame... it was starting to get better)
I plan on visiting Magic Mountain soon though, now that Tatsu is out. would be fun to go to.