Depends what you want the RIB for.
For Dive and Safety use the Humber Destroyer.
But Osprey Vipers are much better handling and make a better cruising RIB by far.
Suzuki DF140s are allegedly a bit underpowered (ie not really a 140) but users report good economy. They are quiet, but like most 4-stroke engines they sound a bit sort of asthmatic if you're used to a two-stroke! Mercury Optimaxes are great engines, very good performance and very reasonable economy. Need to be well looked after though. 5 years old doesn't mean much unless you know the total running hours. Some reckon they are a bit noisy, but most owners love the deep growl (and the scream as the prop leaves the water!)
What car do you drive? If you have a Daihatsu Sirion or a PT Cruiser, the Humber's for you!
But of you drive a Scooby or an Evo you will want the Osprey with the Mercury Opti.