When I began aikido four months ago I found the nearest dojo and whent to an free introduction class. I felt very welcome in the dojo it had a nice atmosphere, and after an hour of stumbling over my own feet and smashing my face
into mat when trying to do a breakfall I knew this was the place I was looking for, and I have only grown funder of my dojo.
So my choice of dojo was based on my intuition influenced by a (one) great expirience, and I don't know how else I could have evaluated the dojo.
I hope your intuition will guide you as good as mine.