I used to run a PowerDrive on one of my boats, so I do understand a little about the two different trolling motors.
First of all, the Terrova is available in configurations of up to 36 volts and 101 pounds of thrust. A PowerDrive is limited to 24 volts and 70 pounds of thrust.
Another significant difference is in the foot pedal. The Terrova foot pedal operates in the traditional forward/backward motion, consistant with any other trolling motor. The PowerDrive's foot pedal operates with a side to side motion, press left to turn left, press right to turn right. Personally, that was ALWAYS one thing that drove me nuts when I had mine.
They both can be upgraded with AutoPilot and i-Pilot. They both have composite shafts, can be bought with Universal Sonar and all units have the digital maximiser to extend battery life.
Both stow/deploy the same and both are available in 12 volt, 55 pound thrust models.
With both, in order to get 55 pounds of thrust, you're going to have to get the 55 inch shaft model.
I've been told that the Terrova steering is quicker to react, but I've never owned one, so I couldn't comment on that. But I did find that the PowerDrive worked quick enough for me.
The Terrova is also about $200 higher in price, if that's something that's going to be important.
So I guess, if money is no object, all you have to do is figure out which foot pedal is going to make more sense for you!
Does that help?