The Athlon is a good bit better all around. It is more modern and uses AM4 and DDR4. It has 4 cores and 4 threads clocked at 3.5ghz with a 3.8 turbo.
I think the Athlon may be FX-based, which is a big downfall.
The Pentium G3220 has only 2 cores and threads and 3ghz clock. It is Haswell based, so it may have a 1 thread advantage, but I cant suggest a 2t cpu for really any use.
Eeesh... the Athlon would be the better choice here... but why are you not considering the Athlon 200GE? It is around the same price and is 10% faster. Heck for just $40 more there is the Ryzen 2 2200G which is WAY faster than any of them.
But, yeah the Athlon x4 950 is about 25% faster than the Pentium.