Well I suppose I'll add my voice to the cacophony.
I went through the exact same debate when I was looking at what to get, and eventually the price point is what was the deciding factor for me. Yes, in nearly every way, the Sprinter is a superior vehicle to the AWD Express van. I don't really think anyone can deny that. It's a simple case of you get what you pay for. However, that being said, different people have different requirements, and different standards. For me, there where a few things that where non-negotiable. I wanted AWD, I wanted the whole build to be cheap, and I had to source it fast. Obviously, I went with the Express. I bought a 2004 AWD Express and in the space of two months built it out and was on the road for right about $10,000. Which I noticed earlier in the thread was your budget.
Before really heading out I did several weekend trips in it, and as of yesterday, just got back from living out of it for three and a half weeks. Although I can easily live with the way the van is and indeed find it rather comfortable, there are things that would certainly be nice to have. I'm 6'5" and the ability to stand up would be amazing! But then I come back to my priorities. My goal is to see the country, roam from place to place. I don't have the van to hang out in (thought that functionality would be nice) I have it to work as a base camp. Something from which I can roam the country, bike from, ski from, and climb from. And something that doesn't eat into my finances too much. Being able to finance the whole build out of pocket (although many have much deeper pockets) was amazing. And it's met every one of my goals.
It drives nice on the roads, and the AWD is amazing for getting up those snowy passes. I've even taking it out on backwoods roads with 4-6" of snow on them with inclines of perhaps 20 degrees and you can stop on the incline and then keep moving extremely easily.
The gas mileage while not being incredibly high is still perfectly reasonable for what it is.
The amount of space it has is perfectly adequate. I carry all of my gear, for every season in it, and I have space left over. This includes keeping my mountain bike in the interior.
The comment someone made earlier about always being on your knees is silly. Yes I may always be sitting or lying on the bed, but I never have to move around on my knees. It's not that short.
The essence of the debate is simply what your standards are. From my perspective, if I had the time and money I would build out a nice high top sprinter with some form of 4x4 conversion. Indeed I've already begun my plans for a build in the distant future. However, that time is not on me right now. And so I have an Express. Which I love! With my expectations, I find it to be comfortable, homey, and the perfect vehicle for me to be on the road in right now. I guess I haven't really said anything that hasn't already been said, but this is just my personal experience with the exact thing your'e discussing.
Also, almost all of my camping in it has been done in below freezing temperatures, with an average of 15° and as low as -20°. If you have any specific questions feel free to message me, or check out my vans thread.
Cheers!