Shoot them both and see which gives you the best groups. Then the one that performs better would be my choice. I like the TMZ and hae taken two deer with them. I like the 290 gr though, they seem to shoot better out of my triumph than the 250.
I use the 250 grain TMZ in my Savage....it has been the most effective Whitetail bullet I have ever shot out of a muzzleloader.....and I have been hunting with muzzleloaders for 27 years.....I understand that accuracy can be tricky with this bullet but my rifle shoots them very well.