Personally, I find DB Pro a whole lot easier to work with than Unreal, from a programming point of view. Unreal is awful code wise - I really can't get on with it. It's been awhile since I tried Unity, but it is in a similar boat, although the coding is more approachable than Unreal.
DB Pro is pretty capable and in honesty for an FPS probably fast enough. On modern systems DB will run pretty quickly these days. In fact I reckon a well written DB FPS would easily beat Game Guru in every area. You have much more control over things and I think the speed would be better (going from old demos I worked on, they all run like silk on my machine). You can use the original FPSC as an editor if you wish, with only one command to load up your entire level, collision and all, which is pretty cool.
It depends as said on what you are after. If you want all the bells and whistles you probably want to try one of the harder solutions. If you have never coded before though, you would be better with DB or Game Guru as both are easier to use than the other options. Game Guru being easier than all of them to get going.
SPECS: Q6600 CPU. Nvidia 660GTX. 8 Gig Memory. Win 7.