My recommendation is to buy in the UK before you go. Reasons for this are:
1. You get a UK spec camcorder with a European guarantee
2. US camcorders record in NTSC colour format. UK uses PAL (look on the front of your VCR and next to the VHS sign you'll probably see a little PAL signal). This means that you need NTSC compatible TV, Video, etc to watch or record from a US spec camcorder.
3. You'd be over your single allowance for a single item and would have to pay duty on your return to the UK. Two people cannot pool their £149 duty allowance to cover a single more expensive item.
4. Prices on the internet are better than than duty free shops, and sometimes better than US prices. Once you've decided on a particular model have a look at the following websites for pricing:
http://www.pricerunner.co.uk/ http://www.dealtime.co.uk/ http://www.kelkoo.co.uk/
5. You get to practice with your camcorder before you get to Disney (always a bonus

)
In terms of what to go for I'd suggest the following:
1. Go for MiniDV tape format as this is by far the most popular. DVD camcorders are still not as reliable and tend to be more expensive
2. Go for a more well known make such as Sony, Panasonic or Canon.
3. Have a look at the following website.. there's loads of useful info...
http://www.camcorderinfo.com/
Hope all this helps.