Not the prettiest vans, but I've got a '06 Toyota Hi-Ace. It's got the new D4D engine and tows 3000kg with no hassle. As it's rear wheel drive it's great on most slipways - pulls my 6m rib and doesn't break a sweat.
Had my mates Discovery lastweek - wow, it tows VERY well!! If it's a 4x4 your going for then I would have one of these myself!
If your sticking to a van go for rear wheel drive as they can pull heavier weights uphill much easier than a front wheel drive - so better on slipways.
The 4x4 transporter is mad money - way too expensive for a van (In my opinion)