If you have an AM2 Motherboard, the 6000+ is a sure bet for compatibility unless the am2 board is cheap and does not support 125W
AM2+ motherboard get the Athlon 250
As for performance, the 250 will perform slightly better and suck down A LOT less power.
It depends mostly on if you have a mobo you want to use already and what it supports... other then that the 6000+ is old.
I'm replacing both the CPU and MOBO so I guess it makes sense to upgrade both to the AM3 to ensure compatability and if I can save a little (or a lot) of power in the process even better !