Heres about how it breaks down... I have omitted the things that are simmilar or the same from this list.

TACTICS
-Pros
Engrossing storyline, Huge class system including a very nice ability system-similar in some ways to FFV,Replay value up the wazoo EXCELENT AI, Slightly better graphics.

-Variables (Depends on what you like)
Some party memebers are never controlable
VERY CHALLENGING

-Cons
Not very portable
Not allowed to go on "missions" yourself
Some of the dialogue doesn't fit together perfectly
The way its set up the view isn't always conductive to good tactical decisions - usually not a problem but VERY rarely can cause frustration when you feel you can't see the whole picture.

FFTA
-Pros
Very Portable, addictive in some ways, good graphics for its system, good ability system similar to FFIX, battlefield is always easy to view, creative reinterpretation of the ff worldview

-Variaibles
Class system is divided by characters race, for example humans can't be dragoons, only bangaa can. Law system is... Controversial. Story starts a bit slow, but builds pace.

-Cons
AI is pretty stupid, capable of only very basic tactical manuvers. Some abilities make it easy to turn your characters into walking tanks, regardless of class or level, and though the law system cuts into this a little, for the most part gameplay can be a little too... easy. Square BLATANTLY plugs the final fantasy series in the opening lines, which kind of biased me against this game from the start, but hey, this is all my opinion anyway, so take it with a grain of salt.