With so much talk about who will be the best agent for you, I'd like to suggest a quick and simple test:
Call an agent on his or her cell phone . . .
Did they answer?
If they don't answer, it's okay! They may be conversing with an actual human being at the time of your call - and we all know that it is rude to ignore the person in front of you to dive for your phone.
However, leave a message then get on with your day while you wait for a return call.
You should find that the agent will return your call within a reasonable amount of time at their next opportunity.
After all, even the greatest agent in the world won't do you much good if you can never get a hold of them!