i3 for upgrade path, however if you want to hpe that amd are going to be releasing better cpu's in the future (like i did) then i would say its your choice.
have a look at thishttp://www.anandtech.com/bench/Product/102?vs=289
they both seem to be about equal, one last thing to not is that the i3 cant be overclocked by using changing the multiplier as it is locked. you can overclcok the i3 but it is a very long and hard process that leaves you unhappy with the results. on the phenom you can simply change the multiplier manually and it will oc easy.