Part of my drysuit course was "how to select a drysuit and options." It's usually a hindsight thing, though, as most (though I suspect not all) students show up for class with their own drysuits. Still, it makes me think that it couldn't hurt to make contact with an instructor (or two) in your area first, and see what they prefer. Sure, different shops will push different brands, so you know you have to weigh all the information from all sources before you make a decision. I chose Santi because the GUE crowd I dived with--instructors especially--dive Santi. But there are lots of good brands.
And as KevinNM said, if at all possible, get measured at a dive shop by people who sell lots of drysuits, who themselves dive that brand, and therefore know what they are doing. (Maybe the same people include your drysuit instructor.) They can help you decide on options and, most importantly, take responsibility for errors in the order. I measured myself at home using what I thought was a very precise measuring chart from the manufacturer, and went through the entire process several times to ensure no errors. Yet there were errors with my order, and I attributed them to other parties involved--manufacturer, distributor, etc. My complaint bounced back and forth for months among the dealer, manufacturer, distributor and me, with no one taking responsibility, until the dealer and I finally reached a sort of settlement. Never again for me.
