To be fair, Onlybbguns is probably the best of a bad bunch when it comes to the bbguns sites. I would not recommend that someone who doesn't know what they're after uses them though as a lot of their guns are not skirmishable. They do at least try to advise people which are skirmishable and which are for backyard plinking unlike some other sites.
Before you buy guns, find a site to play at and give it a go with a hire gun. If you enjoy yourself then there are 2 options:
-If you are over 18, go 2 more times minimum over 2 months and get UKARA registration so that you can buy non-2 tone guns and use that time to research what sort of gun you like. Drool over web sites, ask questions on forums, talk to other players and ask to try holding different guns until you know what is the best gun for you. If you are under 18 you cannot buy non 2 tone. Consider taking a parent along so they can get registered and buy your dream gun for you.
-Buy a gun and get it 2 toned. Most retailers will paint the gun for you either free or for a small charge.
In most cases you will want to get an electric rifle (AEG) 1st. Most people want an M4 and there is no question that G&G's combat machine range is by far the best beginners gun if you want an M4. The only time I would suggest starting with a pistol is if your local site is an indoor CQB (close quarters battle) style one. If you want a dirt cheap 2 tone pistol for CQB then the HFC Mk23 Socom is pretty decent. I actually bought mine from onlybbguns and it has claimed a very high number of kills in CQB.
For outdoor sites, pistols are just extra toys to play with so most people will prefer a gas blowback pistol as they are cooler with moving slides etc. Pistols will not have the range needed to do much good. If your local site is woodland just don't bother with a pistol.