My thoughts on the various razor materials, obviously subjective, YMMV:
Zamak aka pot metal - It's cheap and not very durable if you drop it, but with a bit of care will last as long as the plating does. Compromised plating will lead to water getting to the actual metal and rotting it. They're not bad per se, but not likely to be a lifetime option. They tend not to be too expensive though so maybe it balances out.
Brass - Arguably the best material to make a razor out of. Plenty durable enough (I own at least two near-century-old Gillettes) tends to be inexpensive and very resistant to corrosion. Downsides are that if it isn't plated it will discolour badly and brass can smell, although this seems to be something some people are sensitive to and others aren't. I dislike it. However when plated, as the old Gillettes, it will stay bright and shiny and if there is any plate loss it'll be unsightly but the razor will be just fine.
Aluminium - Very lightweight, durable enough and very corrosion resistant especially when anodised. Personally I'm not a fan of aluminium razors, I've tried a couple and while I like the idea of them I prefer a bit more weight to actually shave with. They do come in pretty colours though.
Stainless steel - My personal favourite. Slightly lighter in weight than brass but still with a nice heft. Doesn't need to be plated or coated and will keep its finish with minimal care. Stainless is not impervious to rust but I've never had a razor rust ever and I'm a run it under the tap when done and leave it until next time guy. Blades are loaded once and stay there until they're replaced. A note on steel grades - 303 / 304 stainless is used for things like bollards and handrails on stairs that are exposed to the elements 24 / 7. The A-frame at the back of the Atlantic 85 lifeboat I was crew on is bare 303 stainless steel and that was also getting regular exposure to seawater. 303 / 304 is more than good enough to make a razor out of. 316 (aka marine stainless) is often touted as a "better" steel for a razor - it isn't. 316 is more resistant to acids and saltwater corrosion but these are not conditions that your average razor is going to face, and it terms of saltwater 316 is typically used for things that are expected to be immersed in the stuff. See earlier comment about the A-frame on the lifeboat. It is a bit of a personal bugbear when someone claims that razor A is better than razor B because it's 316 because it's simply not true.
Titanium - Very tough, almost impervious to corrosion, looks lovely and costs an arm and a leg. Lighter than brass and steel.
These are roughly in ascending order of cost but it varies from manufacturer to manufacturer. With the sole exception of weight, which is very much personal preference, no material shaves better than any other - what you're paying for is the cost of the material itself and how much of a PITA it is to work with. I prefer stainless steel over brass but my favourite razor is the Karve CB OC B-plate and that's because it shaves a lot like a Gillette New LC. Which is brass. More exotic materials will not buy you a better shave.
Ultimately there is absolutely nothing wrong with buying an expensive razor, titanium or otherwise, as long as you realise that it is very likely not going to shave better than a £15 user-grade Gillette, it's just going to look prettier.
