Both fill in that hard to fill space between the trigger guard and the grip well.
I used a Tyler T Grip Adaptor for years on my back up J Frame S&W as a LEO . With it I was able to keep the low profile factory wood grips on the gun.
I kind of like the yesteryear look to the T Grip too.
Some models of the Pachmayr grip had too much rubber over the backstrap of the pistol, I guess to moderate recoil. It interfered with my double action trigger control on K and N frame Smiths. Probably not an issue for those with big hands, but I seldom use them for that reason.