Although long term FX-6300 will be better. It should age slower then phenom that is already old chip. Good with great value ofc but old. FX-6300 is more modern CPU with support for more instructions. Over time support from software for more logical processors will certainly come along the usage of newer instruction sets. That is worth it if you are planing to use it for long time 3 to 5 years and such. In terms of overclocking both chips are equally capable tbh.
I would say they are equally worth in terms of price to performance but they belong in different segments. For example: Get phenom if you are getting up to 150$ GPU aka 7790 and 650ti etc. If you are getting 200$ GPU aka 7850 660thx 7870 and such i would go with FX-6300. If you go with more then 250$ GPU then you should be looking at FX-83xx or i5. And above 400$ and such i guess heavy overclocking of FX-83xx or i7.