The more the merrier!
My general advice is "cast a wide net." Buy as many as you can, as cheaply as you can, and decide for yourself which ones you like. There are a few that will be nigh-universally suggested (The Secrets of Power trilogy, anything by Nigel Findley), but for the most part, taste is wildly subjective. Some folks really dig certain books and characters and writers, other folks hate the same, and both groups are absolutely right (because we're only talking opinion). The simple truth is only you can decide which paperbacks you dig, and to me the best way to figure that out is to buy as many as possible, while spending as little money as ethical; eBay time, used book store time, that sort of thing.
I regularly do eBay searches for "Shadowrun lot," to this day, and snatch up whatever I find if it's something I need. Buy in bulk, buy cheap, and have fun. There are a lot of stories out there, decide which ones you like!
