Don't go for a Mac for gaming purposes - many sources/people can argue against Macs as gaming computers.
Don't go for a laptop. You want something that you can personally upgrade without any hassle, and definitely not have to worry about space. Buy a desktop, buy a decent GPU and bobs your uncle.
I personally purchased my desktop for £400 - no monitor/good GPU included. However it came with 8gb of ram and a decent CPU (FX-4100). I purchased 1 monitor for £50 which is 20", and recently purchased a 24" for recording purposes (youtube). I now use duel montiors. I then purchased my GPU which is the 7770, and get about 200-250 FPS on the HIGHEST settings. On the lowest while mining in singleplayer, I have reached 1200 FPS.
Overall, I spent about £700 and my PC is more then good enough to do anything...
Don't buy a laptop. Save up, get a good PC and you won't regret it.