OP, both of the rifles you describe are desirable, usually well made and if in VG to EXC condition, shootable as well as functional. With proper due diligence, they can be hand loaded to be surprisingly accurate.
You don't state whether you're interested in carbine lengths or musket lengths, both of which are available in the types you mentioned.
The Martini is a bit easier and quicker to use and it's a later design. With a bit of research, parts are mostly still available.
The Rolling blocks are of earlier design, a bit more awkward to load/unload and again, parts are available but more difficult to find, if you don't know where to start looking.
That being said, you may also want a specific contractor for either rifle, say US, Swedish, British and others.
What it will boil down to might be factory cartridge availability.
In the end, the rifle you should acquire should be the design that most suits YOUR sensibilities. It should appeal to you aesthetically as well as ergonomically. Those two priorities have always motivated my decisions when I've had to choose which one I will acquire.
The Remington Rolling Block is relatively easy to find brass/dies and even factory cast bullets for. The Martini, usually in 577-450 isn't difficult to procure components for but sometimes you will have a long wait for the orders to be filled.
Martinis are also available in 303 British and the original cartridges for them were loaded with BLACK POWDER. They come with both Metford and Enfield style rifling. They can be a hoot to load with heavy cast lead bullets and a compressed charge of 4f black powder.
Still, my advice is to purchase the type you like the look and feel of. Some folks don't appreciate the lines of the Remington Rolling Blocks and some don't appreciate Martinis.
RBs tend to generate more recoil, because of the severe drop of the comb on the butt. The Carl Gustov built RBs have a decent sized butt, which helps. Some of the others, not so much.