ESO is my favorite. I've used Zoll Tablet PCR, High Plains, and HealthWare regularly and demoed ImageTrend and another one I don't remember. The ability to transfer a trip is pretty cool- I can receive demographics, meds/hx/allergies, procedures, vitals, etc. from fire and I can transmit it to another crew if I'm working a non-transport role or I can send it to the transport crew. It's also good about importing patients from previous contacts, which is nice.
If your hospitals use the Health Data Exchange, you can also see dispos, discharge diagnosis, and some other info depending on the facility. I'm a HUGE fan of this.
I don't do QA, but the people that do rave about ESO on the back end for that. Our billing is outsourced, so I have no idea if they like it or not, other than they want us to get chart/account/visit/whatever numbers in the trip so they can get billing info through HDE.
ESO is pretty dependent on getting regular app updates and our IT department sucks at that, so bear that in mind.
NPO makes a good point about local set-up. I've found a lot of the stuff I find irritating is NEMSIS 3.0 :shrug: