I think the debate about which is the 'best' is a bit misleading really. I don't particularly see the Kindle Keyboard as an 'upgrade' of the Kindle and certainly don't see the Fire as an upgrade to the KK. They're all different items fitting different needs.
For me, I finally bought a Kindle when the keyboardless version came out mainly because of size. It was finally small enough to fit into all my coat and suit jacket inside pockets. It can even fit in my jeans pocket at a push! (not sure I'd go with that too often though

). The amount of memory and battery size weren't even a consideration for the simple reason that once you go above a week or two it frankly doesn't matter. Similar thing with the memory - for the vast majority of people it's simply not going to be an issue.
However, it suits my usage profile but may well not suit other people's. If you don't always read books in a linear way for instance, or you use the dictionary a lot then it makes complete sense to go for the KK. Equally, if you have a huge number of books or the ones you use have diagrams or pictures making them larger then the KK may be the better choice.
If you travel abroad a lot then 3G makes sense, or if you are often away from home or make lots of impulse purchases then, again, it makes sense. I think it's useful for people who use their Kindle to subscribe to newspapers or magazines as well, especially if you read them on your commute.
As far as the Fire is concerned, I think it's not really comparable to the 'normal' Kindles. I can understand why at first glance a lot of people will think it's an upgrade because of the better specs, but it has two major problems that blow it out of the water as an option (even if it were available in the UK!) as far as I'm concerned:
1. Its screen. I find eink so much better to read for extended periods that I wouldn't even consider a backlit reader.
2. The battery life. I don't want to have to be worrying about charging my 'book' on a daily basis. I've got enough on worrying about charging phones and laptops!
So as far as I'm concerned the Kindle Fire isn't really competing with the other Kindles, it's competing with the iPad, Galaxy Tab and all the other tablets out there.
The only one I'm not really sure about is the Touch. I'm not really sure where it fits in to be honest, other than the fact that a lot of people like touch screen devices. I haven't spent much time looking at it though so may be missing the reason other than that!