I'd probably take the 2.2 over the 1.9. Overall, I think they've had less problems. Go for a manual though, because auto boxes are a known weakness on Renaults of all shapes and sizes. If you really feel the need for an automatic, buy another brand of car.
It's also worth noting that many warranties are void the split second that you stick a 'private hire' sign on the side of the car. I'm not sure if this is the case with the Renault one, but it would certainly be worth checking before relying on it.
I understand that most of the 1.9dCi problems are down to insufficiently frequent
changes, and the wrong grade of
being used (even by Renault dealers.) New 1.9dCi's are now sold with a 9K service interval, and I'd probably stick to that on both the 1.9 and 2.2, even if the handbook specifies otherwise.
The factory sat-nav does not allow for user configurable POI's (including speed cameras) as some of the after-fit devices do. It also only offers 2D mapping, has a rather clunky interface and occasionally makes really stupid routing decisions on long journeys. But for local taxi work, it'll do you just fine. If you buy a car that has it fitted, then just stick with that and get one of the cheap GPS speed camera warning gizmos to tell you about the "revenue", sorry, "speed", sorry, "safety" cameras.