Since you asked, here's my opinion;
Fallout 3 is without a doubt the easiest of the series.
Especially with the amount of exploits available in it to get 10 in all of your SPECIAL stats.
However, since Fallout 4 is going to take place in Boston, the closest we've been is the Pitt in one of Fallout 3's DLCs.
With that said, I suggest New Vegas first and here is the reason; Once you get it patched (this is assuming you're playing the PC version), you can download a few mods (read; unofficial patches) that fix alot of the issues that still plague it.
Most of these are minor, so there's that.
Fallout 3 is without a doubt the easiest of the series.
Especially with the amount of exploits available in it to get 10 in all of your SPECIAL stats.
However, since Fallout 4 is going to take place in Boston, the closest we've been is the Pitt in one of Fallout 3's DLCs.
With that said, I suggest New Vegas first and here is the reason; Once you get it patched (this is assuming you're playing the PC version), you can download a few mods (read; unofficial patches) that fix alot of the issues that still plague it.
Most of these are minor, so there's that.