The difference is spead power, and accuracy. A digital servo is much more responsive, reliable, and in most cases alot stronger, they can also be programmed to do just about anything, the only down fall of the digital servos is they eat batteries alot faster, But in my opinion they are alot beter all the way around, I run the hitec 5945 and 5925 on my truck with an 1100mah NIMH 6 volt battery pack, get lots of run time with this set up, but they do eat the juice alot faster then standard servo's. My addvice to you is if your gonna spen $50-60 on a good analog servo, just spend the extra bucks on a good digital servo you will not be disapointed!! I would recomend the hitec 5945mg digital servo to steer any big truck @ 183oz of torque and a transit of .13 @6v, and for only about $75-80 you can pick one up, now if you want the king of steering you need to go with the Airtronic 358 or 359 they run about $110+ but have about 200oz of torque and a transit of something like .08 sec.