The 116bhp 1.7-litre diesel is the pick. It's not fast but it does pull strongly from low revs, even in the taller gears, so it rarely leaves you wanting.
That said, if you're planning to use the Hyundai Tucson to tow, the 134bhp 2.0-litre is probably a better choice; it isn’t that much quicker, but it does have even more low-down pulling power. The 183bhp 2.0 diesel is slightly faster again, but not by enough to make it worth the premium.
We've yet to try the entry-level 1.6-litre petrol but, from our experience of it in other cars, its relative lack of torque is likely to prove frustrating. The more flexible, turbocharged 1.6-litre T-GDi is the petrol engine of choice, then, but it's only available in the higher trims and consequently quite expensive.