Rudder or skeg. Fiberglass or plastic. Recreational, day touring, touring, speed, capacity, length, initial stability, secondary stability, balance, chine ... aaaaaahh! Who knew kayaks were so complicated?
I tend to over analyze every significant purchase and buying my first sea kayak was no different. After countless hours of googling the best advice I can offer is to talk to other people who kayak in the area where you intend on paddling.
Shout-out to Brad and Lance at Ramakko's Outdoor Adventure Store in Sudbury, ON. The service was excellent and I was able to "test-drive" a few kayaks prior to buying. At the end of the day I picked up a last year's model Wilderness Systems Tempest 170 at a discounted price and paid no tax. Very happy with the boat so far ... and I must say it looks pretty sharp on top of my car.