It usually depends on these factors in this order:
1. How much time do I have
2. What do I want to accomplish - what is my goal
I never have to wait for a bench. I have been going to the same shooting range for 30 years. I know the woman who owns it, her daughter and her grandaughter - all of whom work there. I usually don't even go inside and check in and pay. I usually do so afterwards when I know how many guns I have actually shot. It's good to be a regular!
To say 'usually', meaning more than any other times without question it is shooting .22's. I never take less than 2 though I may take 2 rifles and 2 or 3 barrels.
I usually have a goal - testing ammo in a barrel, checking how some modification has changed an existing gun, swapping parts between guns or whatever. I am constantly looking for the best mix of changable major parts (barrel, receiver group, trigger group, stock) after all the little stuff is done.
I have found after swapping a LOT of barrels that a certain barrel just shoots better after swapping it to another receiver/trigger/stock. Once I find the best combination, I generally try to keep those components together with the label of it's favorite load attached or inserted somewhere that I can see easily. As far as ammo amount, I have rimfire ammo separated into plastic carry boxes about the size of a 50BMG box. One for .22LR, hunting/plinking, one for .22LR match, one for .17HMR. I guess I'll have to get another one for .22HM2 here pretty soon. They probably hold 1,500 - 2,000 rounds each so I'd say I average that each trip.
Now on the other trips, it is still usually two or more. Whether pistols or rifles or whatever, I still have a goal, even if it is just practice. The only time that I take one is when I am shooting a hunting pistol. One gun, lots of loads.
With CF rifles, 2 or more allow me the opportunity to swap while the one just fired cools off. One thing I have learned is that when I do that I either take 2 rifles of the same caliber or in very different calibers. No need in shoving a 6mm into a .243 or .270 into a 7mm mag, you know.