I would recomend the DS. It has excellent games besides the two you mentioned. The FF4 remake is excellent. If the Chrono Trigger DS version is just like the SNES version then it is without a doubt AAA. Plus you'll have excellent games to play on the go.
I played played some of the SNES FF games on PS1 and in all honesty yes the load times ruin them. Would the load times be cut if you were to try them on your PS3? I have yet to try. But give it a shot. All PS3's will play PS1 games. Not just the original 60 and 20 gigs. But if you still get load times then it's DS FTW.
I have Castlevania SOTN on my PS3 and the loads are still there, most likely they will be for FF as well.