Let's face it, they use 7.5 ton lorries in the States. We have a jumbo transit and a swb transit (very different machines in the back) and overall I would go for the jumbo. We are quite rural so a jumbo or a Luton in town may be difficult.
If you have heavy kit (RX20, back up portable, curtain machine, big dehums etc) the Luton may be a no go area if your back is like mine.