I have an older 74# 24v Maxxum with variable speed. It replaced a 12v 55# Motorguide fixed speed. Besides the increased power, the next best thing that I'll be hard pressed to live without going forward is the variable speed. Much nicer than a fixed speed TM.
Also, I'd get the highest # rated your budget allows and that you can fit on your boat. I ran a 55# for years on my local river. Was constantly fighting current and many times the 55# couldn't hack it. The 74# is much more suited for my needs. But there are still times that an 80# or even 112# would be nice.