Most reliable transit van 2001-2004?

I'm looking to buy a ford transit van for my landscaping company either swb or lwb not really to bothered. I just want to know what the best most reliable engine is to go for? I would like a little bit of poke but not essential would rather reliability.

You're talking about 10 year old+ used & abused commercial vehicles. A Transit van is lucky if it LASTS 10 years. They also rust like hell.
Concentrate on finding one in good condition and don't worry about what engine is in it.

Chat to those whom run such vehicles. Actually these are rated as best vans ever despite bias from those whom have not checked selling and reliability data.
limited range of engines. Larger capacity tend to be slightly less overworked. Look at spares costs. Etc
rust is very much down to lack of maintenance etc. 10 years is a long time in commercial world and high mileages and abuse is common by those whom drive them.
if we can get a van with one owner or three at most with full service history? Then we likely have a decent vehicle. Lack of servicing is major cause of failures.
check out used vehicles in commercial sector. These vans are fairly basic and as such spares and repairs are readily available.