I have one of each and would probably go with the Tantal for less maintenance. I have read of the C-93 to have the bolt gap close up too much and be out of spec once you shoot it a bit and all the parts settle it. That can be remedied by oversize bolt rollers but is extra time, $ and hassle. I only put a couple mags through mine and the bolt gap is on the low end of acceptable, so I'll keep an eye on it. That said it's really nice to shoot and you can get mags reasonably priced from Midway.
If you go with a Tantal, I'd get one from Atlantic Firearms (like I did) that sells ones assembled by Interarms and have the original chrome barrel. The ones Century puts out have a new barrel that is not chrome lined and at least the early ones had the wrong bore diameter that caused keyholing of the bullets. The only problem I had with mine was the roll pin they used to secure the bolt piston started to walk out but a tap with a punch to spread it out more cured that.
Both are a lot of fun, but I think I'd trust the Tantal a bit more (but that is just my subjective opinion).