"John, both the 50 and the 90
"John, both the 50 and the 90 are excellent motors with a decent history. They are however the last of the 2 strokes still being produced by Merc and the word is, their days are numbered.
Having said that, I would still buy either without an issue or second thought. They are however, just as loud as any two stroke out there.
Depending what you plan to use the boat for, you may be dissappointed with the 50. It will push along a 16 1/2 footer nicely to get you to a fishing spot, but if you plan on pulling a tube, wakeboard etc, you would really want the 90.
Ditto if speed is what you are after, the 90 wins.
For trolling you would mostly likely need a trolling plate or a kicker motor to get you down where you want to be (with either motor).
From your description it sounds like you are looking at one of the common package deals (legend, tracker etc).
If you are looking for 2 stroke performance but with the sound level of a 4 stroke, I would see if they can package it up with a 75 Optimax...."
A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it :)