I would probably buy the same one that I have now.
It's a Dell and I am more than happy with it.
On the two occasions that I have needed Dell's technical support the problems were delt with quickly.
It's only 8 months old at the moment so I wont be looking to replace it for a couple of years yet but when I do I will probably go to Dell again.(even though I have read a good few horror stories on this forum).
Good luck with whatever company you choose.