Like somebody else pointed out, it really depends on what you shoot them out of.
If you get a 44 Mag of any variety, you know that it is safe you shoot full-house magnum loads.
If you get a 45 Colt, it could be rated for black-powder loads or it could be rated for 44 Mag-ish loads.
For my money, there is no comparison. Get the 44 Mag. If the extra 0.020" is important to you, get a 454 Casull. It's basically a stronger 45 Colt, and all the firearms chambered for it are capable of full-house loads.
Of course, if you're planning to shoot the round in question out of a rifle, you might as well skip the Casull and just get a 45-70. While not exactly equivalent, both cartridges have loads that can produce similar performance.
"... I cannot but conclude the bulk of your [politicians] to be the most pernicious race of little odious vermin that nature ever suffered to crawl upon the surface of the earth." ~ Jonathon Swift