I use Sportdog. I like it because it has 2 tone/beeps. One is supposed to be like a clicker feature, a "good dog" tone, but I never use that (not that they aren't ever good LOL ). I just always use the correct tone.
I love it, it's the 2nd Sportdog I've had and I've been happy with both. Completely waterproof and the one I have now is rechargeable, so no batteries to deal with.
I like Gun Dog Supply- they have excellent customer service and if you call them they will guide you toward the right collar for you based on both price and features. What I've found is the collar you want depends on what you are doing. Do you just want to train a solid recall for off leash? You probably don't need as many levels. Do you want to train advanced OB behaviors- then you might want a collar with completely adjustable levels.
I train with low-level stimulation using Lou Castle's/Michael Ellis/Bart Bellon's techniques to start. But when that part is done, I really don't need a ton of adjustable levels- I'd rather have a "reminder" level, a "correction" level, and a total "avoidance" level (cut off a chase, for example) adjusted to each individual dog's "hardness"- if that is the right word.
So, for that, a device with set levels or without a rotating dial is better- for me anyway- than a Dogtra. It's hard to fiddle around with a three-dog collar and a rotating dial when all three are on a moose, for example. Usually I have gloves on, am out in the woods, etc. and the rotating dial on my Dogtra wasn't ideal for my situation. I do use the Dogtra for initial training.
I actually saved up and am going with the Garmin Alpha for it's tracking/e-collar capabilities. You can program that device specifically for each dog, and even set up alerts when the dog goes outside a certain distance from you or walks outside of a pre-set boundary. But that is probably beyond what most people need or want to spend.
Also- for what it's worth. I personally am not a fan of the vibrate feature. I know people like to not be "shocking" the dog- but my dogs actually hate the vibrate more than the low-level stim. I do like to have a tone feature for the collar- it's great not to have to always use a whistle or yell for the dog to recall. And for those of us who live in the north- a light on the collar is also a nice feature. Just extras you might want to consider when you are choosing the collar. For a one-dog model, I'd plan to spend at least $250 for a good model.
I also called first to get their opinions on the different models. The guy who talked to me suggested that I halve all the distance/range coverage for a more realistic view, regardless of brand/model. He was very helpful.