I just learned last night that the sn754410 does not have kickback back protection diodes like the pin compatible l293d. The diodes in the sn754410 are for ESD protection (I don't know what that means).
ESD = ElectroStatic Discharge
If you walk on eg. nylon carpet and then touches something like an earth connected radiator you are discharging the ElectroStatic charge that you have build up.
ESD is also the phenomenon when you rub a balloon against your clothe and it then clings to walls (or make your hair stand up)
In electronics, ESD can damage devices so that eg. a lead on a silicium chip is partly cut and perhaps days, months or years later, the lead breaks completely from overload in the affected spot.
The flyback protection that you need is to counter the inductive kick from the motor windings, as they deliver quite a high voltage the "wrong way" round and can pack quite a punch.
I'm inclined to only use forward differential drive, but the problem there is the sn754410 does not have braking. This causes the robot to be not so responsive.
motors 12-15V ~50mA no load guessing ~ 500 to 750mA stall, I didn't want to stall the motors to find out exactly
1) If I were to use a higher current h-bridge chip could I switch directions more rapidly without risking blowing anything?
2) Recommendations of any motor drivers that have braking? over current protection would be nice too.
Just add the flyback diodes and then change your code to force a pause when going from one rotational direction to the opposite.
If you think you need more, you can put 15V..25V tranzorbs/transils in parallel with the flyback diodes but mounted as close to the motor terminals as possible (you allready put caps there, right?)