In my personal opinion there is little, if any need for a pistol in a skirmish situation. Unless you decide to use it on purpose, you'll never use it. Money you have set aside for one would be put to better use upgrading your primary - new barrel, hop rubber/unit, maybe getting some sort of optic, some more mags et cetera.
My pistols have always just ended up weighing me down, emptying my wallet, and taking up space I could use for magazines for my rifle.
If you're going to get one, I'd say to go for something high quality, otherwise you won't be able to guarantee it'll work when you need it to.
Look at Tokyo Marui and KWA for the top end pistols. KJW and Socom Gear if you want something slightly cheaper but less reliable. The HFC pistols are a grade below that in my opinion. They don't get a lot of press but they're in the same sort of league as WE, which isn't high in the ranks.
If you just want it for back garden plinking then I'd say to just buy whatever you like the look of, you can get some relatively ok pistols for back garden use for around the £40-80 mark, since you don't need to worry about reliability all that much when you're not getting shot at you ought to be alright with just about anything.