Also depends if you want an a3 (prices shoot up a lot) Over the years i've found
Epson and HP Very good quality scans, Umax are supposed to be really good but the ones i've seen are flimsy quality, Cannon have a good range of A4's better quality build, and a good range of software manipulation. You will hardly need much above 300dpi for general work. some scanners will do over 4800 dpi, great if you want to blow up a picture the size of your house (didnt think ppi was still around) unless they are on the new photo scanners.