I think a lot of it depends on the skill level of the groups you're with. Titan Hard is probably going to be considerably easier than the other Extreme Primals.

There's also the itemization between the two items to consider. As a BLM, I'd prefer to have ACC on my weapon so that I can move my gear around a bit differently. The Extreme weapon may or may not give that option and the T5 weapon is currently out of my reach, so it's definitely something I would consider getting if it had ACC.