Olympic/AMR works out of Olympia area.
Rural Metro/Falck in the Tacoma/U.P./Lakewood area.
AMR/Falck/Rural Metro can be seen in Seattle and a bit North of Seattle.
Tri-Med works in the Kent/Des Moines area.
Of course, they all do IFT so you'll find them pretty much everywhere.
My understanding is that AMR pays the best but only if you're working out of Seattle or perhaps it's their Tukwila station, otherwise you're subjected to 10-11 USD per hr when working anywhere else with them. Falck by far has the best benefits though and also happens to be the largest EMS company in the world, located on 6 different continents. I think overall Falck pays their employees the most for working out of all locations. Their HQ is in Mountlake Terrace, but once you're done with orientation and training you can work out of Lakewood/Fife/DuPont. Olympic I've only really seen them in Olympia, but I believe they're the only contracted agency for 911 in Thurston County and like FireWA1 they are also in Kitsap but I don't head out that way too much, just seen them making runs across Narrows. Rural Metro I've seen a little everywhere, I think they do 911 in Tacoma but IFT everywhere else, not sure. I know most of their folks moved to Falck about two years ago. Tri-Med is the lowest paying of all but my understanding is that you can get some great experience from them. I do not know what is going on with them though, their owner recently passed. I did however see four new recruits roll into Blumenthals following that, so who knows. I think all the agencies are watching Tri-Med right now.