First of all it depends on how you take it. Now, I personally don't have experience with the Red9 but I do have experience with the Blacktail. The Blacktail is definitely one of the best handguns I've ever seen. Once you tune it all the way, its a beauty. It shoots fast and quick so that will definitely help you when there are more than one ganado or monk or whatever and they are in a big angry mob. My suggestion to you is definitely get the Blacktail. But, that's just my opinion.
do you mean handguns that are in resident evil? well a lot of them are general handguns. the red9 is a german broomhandle. The Chinese version would be a lot cheaper, and rpg's are very, very illegal, don't try to get one of those.
It really depends on you. Let me just say that the infiinte guns don't count. They are already super strong as it is. So, find out what weapons you like and tune them up all the way. This does include getting the exclusive. However, there are guns out there that don't have any exclusive. My best example is the Killer 7. It is a type of Magnum and a good one. It's a long time to get it (a.k.a. the island but it's worth it). This is probably the only gun that doesn't have an exclusive. Personally, I don't think it needs it. Once it's tuned up all the way, you got yourself a very powerful Magnum. So, like I said. It depends on your taste.