Welcome to Flyertalk, forestfarm.

There is really not a lot of choice any more on any given domestic route -- especially if you stick to a particular airline or two. Boeing 737s dominate, with the Airbus A320 series right behind.

On the route you are booking, if you want a nonstop flight there is no choice as trooper points out. A Boeing 737 is your sole option.

When you look up flight options online the aircraft type is usually shown and you can usually click to see how booked up your particular flight is.

You should also take a look at Seatguru.com to see the cabin layouts for each airline. If you are shopping for comfort in economy class, get familiar with the concept of "pitch" -- that's the distance between rows of seats. The more pitch, the greater your legroom. A cabin with 29" or 30" pitch is not too comfortable. A JetBlue cabin with 34" pitch is more comfortable, but they don't fly to Fairbanks. If a particular cabin has any especially bad seats, Seatguru will flag them for you.