The SMB uses 4.10s. I don't know about the Quigley.
3.73 gears are "taller" than 4.10, and 4.10s would referred to as "lower"... just to get the terminology out of the way. They are changed by changing the ring and pinion (R&P) which are the gears inside your axle pumpkin.
If you look at a chart such as this one
you'll see that as you go up in tire size, to maintain the same ratio you need to have lower gears.
So for the same size tires, 3.73 give you better gas mileage, and 4.10 give you more power. With the automatic transmission the "power" end is less noticeable as the torque converter helps out.
Reasons for going with 4.10s are:
Towing, having more low end helps get the trailer going
Larger tires, having more low end helps get the tires going
Offroading, having more low end means your engine brake is more effective and over all gearing is lower
Performance, having more low end means you can take off quicker
The reason to get 4.10s when you get lockers is that the labor for doing them is combined- since you have to take the ring and pinion out anyway to do the locker. If you do the lockers and later decide to do the gears or vice versa, you're paying twice. If you don't need more power or lower gears, and don't expect to- (e.g. larger tires in the next two years) there is no reason to change the gears.
Oh yeah, and you have to do gears in both axles so they match.... where as you can do lockers separately.