Vans seem to fall into one of 2 camps either brand spanking with a massive discount (pre reg with 6 miles on clock are still brand new) or an old un for under £2000 then you no mans land which is stuff a few years old which when compared to the deals you can get on new aint such a good idea.
Lease or buy depends on individual circumstances and what your own accountant says
EG ..... you got £12000 taxable profits sitting in the bank then you prob going want to buy outright and claim against your AIA (annual investment allowance) therefore writing the whole lot off in 1 go.
or
your skint but van is shagged and dying then with a 3 payments up front lease is going to look attractive esp as its 100% tax allowable ... ok you will have to swallow vat if not registered but still prob cheapest way to aquire a new van.
or
what I seem to have done is to buy an old van for £2000 with a decent mot and history and decent bodywork run it with no payments but stick £30 a month to 1 side in the "maintenance" kitty
were all different so no right or wrong way I would suggest.