Depends how much you want to spend as well. If you go for horde army like skaven or orcs gonna burn your wallet more, so do as I do and hit eBay with a snipe tool like Gixen. Built large Skaven army 6 x clanrats unit (4 plastic 2 metal), 8 rat ogres (50:50 metal/plastic), 24 rats, WL Cannon, 2 Plastic PMOnks 1 Metal P Monks, 90% of special characters, 2 metal slave units, Screaming Bell OOP One, Plague Censors x 12, Globadiers x 12, 4 assasins, Stormvermi Unit (Classic one), 5 Ratling Guns, 5 Warp Fire Throwers, 12 Gutter Runners, 12 Night Runners, 4 x Jezzails from 75% eBay - cost about £125 and some of the best classic models. Total model count c.275-300 figures excluding big items
Just Gotta paint the things now
I personnally love Dark Elves and am re-doing mine with modern and old Marauder figures and selling of 80\'s stuff.
Next for me is Chaos as less models to get and quite forgiving in battle and love all the fluff