I bought a Phil and Ted Sport when I had my daughter 2.5 years ago. I used it daily (putting at least 1k on it) as a walking stroller--only one flat! I had my son 10 months ago, and the first time I put the jump seat on it, I laughed myself silly. It is the cleverest thing in the world. Seriously. No instruction manual, a pain to use, but man is it a great stroller!
I always loved my stroller (it handles snow like a champ!), but when I made the bassinet and put the jump on the front of the stroller (skipping the car seat attachment completely), I was just so amazed by it.
I LOVE it. It's light weight, fits in the trunk of a civic, and handles great in small bathrooms.
I have seen some really great other doubles out there now. Lots of new stuff since I purchased mine.... I'm not familiar with the others you are asking about, but I do recommend going as compact as possible, you will need it if you are big on going places with your kids. Bathrooms are small. Trust me, even if you baby-carry (which I do), you will need a small enough stroller to handle bathrooms.
One last thing,P and T have been doing this for a while. It's a great single stroller, it's a great double stroller. It is a terrific all-terrain stroller.
I just quickly looked at the Explorer. It seems to solve the biggest problems with the older versions (needing two hands to fold it, etc). I am sure it's a great stroller, especially since it's just the older versions updated with more conveniences. Look out for good sales. Some of the online retailers do 20% sale with new models (just picked up the latest Britax convertible for my son at a great price).
Now, the question is this: would I have paid that much money if I was just on the market for a double, i.e. I hadn't purchased it before I had my first? Hmm that's a hard one. My daughter is at the point where she really just wants to walk (21 months apart in age). The jump is great in that she can just climb in the back if she is tired. And I love it as a single stroller, so YES. I would. I wouldn't buy a double that isn't a jump seat convert because most of the time you will be using it as a single, with the occasional extra passenger.
I can tell you that a friend of mine has a Baby Jogger and she LOVES it. She has the side-by-side.
I'm sure you can't really go wrong with any of them. You are right in wanting a removable second seat. It really is the way to go. To the best of my knowledge, P and T invented the jump seat.