I bought a new long arm in January. I have a Pfaff PowerQuilter P3 with computer. I chose this machine after a great deal of research because it came with unlimited training classes. I have to be honest, I'm still struggling. I'm not sure why piecing, cutting, pressing etc came easily to me but long arming is such a challenge.
If I'd purchased a used machine or one that didn't come with classes, I would be sunk. It amazes me how many people here can just figure out these machines but for some reason it's a struggle for me.
My best advice is to take your time and do your research. If you can, go to a big quilt show where there will be vendors for multiple brands of long arms. Try as many as possible. Take a notebook and jot down what you did and didn't like about each. Sometimes, using one machine will make you realize you need to go back and look at another to see if it had a particular feature you like. Often you can get a sale price if you purchase at a show.
If you can rent time on a machine, that's great. It not only gives you experience, but it gives you time to see what features are must haves for you and which aren't so important to you.
Good luck and keep us updated!