As always, the make and model of the car or van is irrelevant - it's the specific year, engine, gearbox and specification that makes it worth buying.
Many vehicles have fundamental flaws - in engines, gearboxes and electrical systems that are well documented when a few years old - eg ford wet belts, any number of VW diesels, anything with electronic gearboxes etc. Plus the VED for some combinations can be punative.
I can't advise on Vans, but with cars I never buy newer than 5 years old - easy to identify the lemons - even if you have bad luck with what is a generally reliable model and the engine goes bang, the scrapyards will be piled high with cheap replacements.
Currently have a 15 year old VW 1.9Tdi owned for 6 years and engine runs like new - owes us nothing if it blew up tomorrow.
Other car is an Infinity - a bastardised Merc A class - which does have some minor documented faults eg heated seats fail (ours has but I don't really care), fancy led headlights on some models - cost up to £1,000 to fix (ours had £3.99 halogen bulbs - but you still need to take the wheel off to replace) etc.
The engine is a Renault 1.5 diesel as fitted to Dacia dustbins, Nissan Quashqai etc - fairly bulletproof proof for a modern diesel but £400 quid for a replacement from a scrappy if not.
There's a myth around transporters - people run them as a hobby and (fortunately) love spending money on them.