It all depends on Price and warranty:
I would go with DELL, or ACD's. Unless you find a better deal.
roomate bought a Samsung 20" DVI LCD for his Powerbook. Cost him $500 Retail @ Best buy cause he hates waiting for anything to be delivered.
I found the same display online a week later for $320 SHIPPED
I think with Samsung you get a 3 year warranty.
With the Dell 20" you can get coupons that bring the price down even more from their posted price of around $370ish. YOU can get a warranty of 5 Years with the dell displays for a tiny extra cost. Thats more than worth it.
24" is around $750
30" for $1700
All are almost identical to the ACD except for the casings and USB Ports.