Select a realtor the way anybody should- interview carefully, choose wisely and act in your own interests.
I would think you actually have an advantage because you have seen many agents in action and you must know the great, not so great and everything in-between.
You have to not worry about agents' feelings at this point. A good agent (and decent person) will not withhold business from you just because you chose someone else.
as a Realtor who's been in the position of not-chosen, before. I'd say the least painful answer was "I gave it to her, because she works in my area, deals in my kind of properties, successfully, and has brought me the most business (ie: she'd referred more loans to him than I had)...
a reasonable "pick", in my mind.
However If it were me, I would have some fun with it. I would invite some over to your house for drinks, and horsey durvers and have a drawing. Turn it into a party. It would also serve as a sort of brokers preview.
I have a niche market and specialize in marketing older properties. If there is an agent who specializes in your neighborhood, style of home, or even an agent that specializes in working with Mortgage Lenders, then you will be able to clearly explain why you have chosen to work with them.
Ask all of your favorites if they'd like to interview for the job. Tell them you want to see their marketing plan and compare them to each other.
Search a couple of their current listings on line.
Use concrete reasons why you pick the one you do. It's like an essay contest. If you give them all a shot, they can't be mad.
Or.....Use someone you don't even know!