I think that most everyone will encourage you to buy the steel frame of your choice if concerned about durability.
The brassers can also last a long time if loads are kept to a happy minimum, and they are made in Colt and Remington models.
Some folks here still do buy brass ones because they either like the Confederate look or they can sometimes be bought at a reduced price.
And some folks figure that they can salvage some parts like the cylinder, grip frame, barrel or internal parts for future use for a project gun, for repair or to sell.
No one has ever scientifcally tested how long a brasser will last because every gun and loading history is different.
One member was loading 30 grains of Pyrodex in his brass 1858 without any problems in the short term.
But in the long run, maybe in 5-10 years he may experience some wear and tear issues.
A Colt brasser may also experience wear & tear issues either sooner or later than that.
Which one to buy really depends on how much a person wants to invest to try it out just to see how much they like firing one and the routine of cleaning it.
The recommended loads for a brasser are closer to 20-25 grains unless you want to buy a .36.
Cleaning is the chore after each shooting session which depending on whether you already have a muzzleloader or not, is part of the routine of shooting black powder guns.
And then there's a few accessories to buy,, maybe a powder measure, a powder flask, a nipple wrench and a capper.
Some of these can be home made or another can be skipped since capping can be done by hand.
Then you need to buy or make powder, caps and balls, and maybe also lubed wads which are optional.
Some of the extra costs add up, again depending on whether you want a holster or not and some cleaning supplies, loading press, screwdrivers or whatever.
Head to the nearest store and try to handle the models that you're interested in and inspect them closely if possible for fit and function before you buy one.
Good luck and don't forget that buying a Colt may turn you into a kitchen gunsmith quicker than you can say Boo!