I trained in it for a couple of years with MAP's Robp.The inital training can be very hard due to no mats being used so you end up black and blue after every session but that soon goes once you learn to relax.Same with strikes,once you relax and don't feel sorry for yourself they don't hurt as much.Its not really a martial art but more a system of survival and I found the training very practical.It wasn't really designed for "winning" a one on one brawl but rather as a method of getting away from that kind of situation.
I say Systema. If you already have experience with other martial arts and you seem to have all 4 ranges covered Systema is great. Systema does not really stress teqniques but the instructors usually have you do unusual exercises that give you mucsle memory and teaches you about the body mechanics of your own body. After these exorcises you practice scenarios (related to the exorcises you just did) where you can use any teqnique you want. Basically, you develop you own personal style (similar to Jeet kune Do) except that you don't really "borrow" from other martial arts so much. It's a great supplement to other martial arts. Really, it's just great exercise. You're body is going to do something different in every lesson. I've taken a hand-full of lessons and have read a lot about it.
If you want some practical application stuff mate I would avoid both Krav and Systyema. I don't know a great deal about systema but it seems to be trying to be very clever and I've never trusted arts that try to be clever. Krav I have had some limited experience in. I was going to take this month long instructors course by the guy on the phone didn't want to give me the time of day so I just saved my money. Its a hitty missy system from what I can fathom, you either get someone good or you don't... so if you decide to try it vet the club seriously. If you want something usable look up a RBSD or Combatives club, again vet seriously though