The G12-75Ts in the 1960 cabinets produce (in my opinion), just slightly more treble than Vintage 30s. And while on the subject, the Mesa Traditional 4x12, slant or straight, with Vintage 30s, has a little more bottom end and oomph than the Marshall 1960 cabinets. The Mesa is just slightly larger, which drops the cabinet resonant frequency a little bit.
I have read that the V30s break up earlier than the G12-75Ts, but I have never noticed this. I play mostly at home, and not very loudly.
Whether you like one speaker-cabinet combination over another depends entirely on the rest of your rig and the music style and tone that you like. The brightness of your guitar pickups, the length of your guitar cord, the number of effects, and your amp head and settings will all influence the tone. Best thing to do is take as much stuff to the guitar store as possible, at least your guitar and maybe even your head and effects, and plug in and give several cabinets a try.
Happy hunting.