Depends how you feel about the other games in the respective series, IMO.
If you liked the previous Burnout games, get either.
If you liked the previous NFS games, don't bother getting Hot Pursuit, because Criterion turned it into a Burnout clone with infuriating rubber-band AI (that the series had only just managed to get rid of before Criterion came along), zero car customisation options and more blatant than ever advertising.