depends on your budget. and i can only offer opinions on the guns i currently on, but my nuprol pioneer defender (approx £110) works well enough for me in both CQB and outdoors out of the box. my one has had a M105 spring and a new hop bucking fitted and runs beautifully with .25s.
i also recently ran my totally stock TM P90 (approx £280) and it had really impressive range on it for such a compact weapon (i didnt measure it out, but i estimate about 40-50 metres...)
my SMC-9 is a good gun if you want to look at gas blowback guns around the £250 mark, however i only ran my one once at an outdoors site as a secondary that only fired a few shots, so i cannot really offer a good opinion on it compared to the p90 in terms of performance, but in terms of size its only a little larger than a p90, but the magazines are a little harder to come by