[CDJ]

Definitely go the G size. Tigs chew through gas. They need pre and post flow to keep the tip in decent condition and a higher flow rate than you'll be used to with the mig.
They also can't be run on CO2 like a mig. You need argon or a argon/helium mix.

Renting is the easiest way since you can just take back the empty and grab a full one.

We empty a G size a few times a year.

Also if you have your own bottle you have all the hassle of keeping it in date.