comparing the EI and Advent I'd say the Advent. More ram, more HD, same processor, DVD drive, enough UBS port. Wireless ready, half hour more battery life. Looks better than the EI. The Medion has some nice features, but it's only half the ram of the Advent, and trust me, running Vista you're gonna want Ram over HD space and a built in microphone.
Personally I've only ever heard of EI. But for your budget,( which is around $780.00 US$) the specs your looking aren't bad.
A lot of it depends on what you need it for. If you're not happy with only 60 gig HD space then I'm sure you can find an external drive cheap somewhere to add on another 20 or 30 gigs. for 50 pounds or so (sorry, I don't know how to make the symbol )....haha or you can go for a 1TB HD for 205 pounds
The only major downfall I see with all 3 is the lack of firewire ports. It's alwasy good to have at least one
So yeah, All in all I would say go with the Advent
(P.S. If any of the currency conversion was wrong, I blame my widgets)