We ran a 4x4 Nissan Navara on a 51 plate until recently when we traded it in for another Transit Tipper. The profit we can make on wasteaways with the tipper as opposed to skip hire was the decision maker for us.
All 4x4s have their upsides and down sides. A double cab gives more flexibility for moving your manpower but sacrifices some of the load space.
Personally we now run Transit Tippers, 1 per team, and if we need smaller vehicles in future we will look for a smaller van such as the Connect for this.
Commercial vehicles also hold their value better than 4x4s historically at least. And if you are looking to maximise your resale value then buy a silver vehicle! It is industry proven that a silver vehicle will realise more on sale than a white one.
The benefits of leasing v buying are something I know about having worked in house for a lease company in their Accident Management department. The only person who can advise you what is right for your business is your accountant, if you have one. If you don't then I would recommend it is worth spending a few hundred pounds on some advice before entering into any lease or HP deal as their advice should save more than their fees.
Personally we like to own all our vehicles outright without finance as then we do not have a loan to service. If this means running older vehicles then you can always put an amount away every month towards the extra servicing and repair costs, but the trade off is no interest to pay and no balloon payment at the end of the term.