At lower levels Yiazmat begins to take exponentially more time to kill, since you're doing less damage and healing more often.

If you have to choose between the two, FF12, while not the best FF ever or anything like that, blows DQ8 out of the water (everyone knows what I think of DQ8 and how I hated that game). FF12 is well worth a play but it's not the first game I'd play. Persona 4 seems the better choice. But, only relative to the question, FF12 without a doubt

FF12. You can't go wrong with a main series FF. Except X-2...

FFX. much better than both.

^Truth.

Personally I prefer Dragon Quest VIII. But what are you looking for? Neither one has a good story (DQ's is cliche, but okay, FF XII's story is just weak).

I think you should get all of these and then we can discuss some more options.

Star Ocean 3
Grandia 2
Grandia 3
DQ 8
FF-X
FF-XII
Tales of the Abyss
Suikoden 3

I think these should tie you over for some time :)

For me it would be DQ 8, i disliked FF12's battle system. But as others have said it really does come down to what type of game you are into.
Would also recommend Beyond good and Evil if you missed it.

Here's my recommendation:

I packed away 60+ hours in Dragon Quest 8 and loved every minute of it.

I somehow put in 35 - 40 hours in Final Fantasy XII, hoping I would start enjoying it at some point - yet every hour seemed like pulling teeth - in the end I ended up saying "f..k it" and quitting - not being able to muster enough interest to finish it...

Just for a point of reference - I adored EVERY Final Fantasy Game until XII - I still replay the old ones to this day.

You should try out both, starting with FFXII. Whose story was better but not exactly what people expected from a FF.

DQVIII is indeed very oldschool, but very nice graphically and funny also.