The bigger, the better. The setup that came with my 89 Ranger had a 3/4 bore unit, now that I've swapped in the V8/Toploader 4 speed, I'm now using a 7/8 bore unit. Those are the only two sizes available to me for the Ranger.
Hydraulics is simple, on the pump side,(master), the larger the bore, the harder you will have to push, but you will get the most travel out of the Slave.
So the smaller the bore, you will have to push easier, but the slave wont travel as far.
The exact opposite is true for the WORK,(SLAVE).
On the MASTER,You want the smallest bore that will give you the travel you need.
Example; If your clutch needs 100 lbs of pressure to move it,
WITH
1" bore master - 1" bore slave = you will have to push 100lbs pressure with your foot, and the slave will travel an inch for every inch of pedal movement.
2" bore master - 1" bore slave = you will have to push 200lbs pressure with your foot, but the slave will travel 2 inches for every inch of master travel.
1/2" bore master - 1" bore slave = you will have to push 50 lbs pressure but hte slave will only travel 1/2 inch per 1 inch of master travel.
Personally I like a hard clutch pedal, so I would go with the Largest Master.