for me it just comes down to money.
4 pot cheaper to run, repair, and insure i would have thought. Plus easier to work on. Cheaper and easier to fit lpg. It would have to be a manual though for me, the auto will sap to much of that lesser power, and i cant be arsed with manuals there days, too much traffic.
You will get more power and a much smoother ride with a v6, much more refined. I have driven 2.0 16v owned 2.5 and now 3.2. The 4 pot suprised me i have to say, it was very reasonable to drive. But i would have this little voice in my head"you should have a got a v6 then, not much more money, and more luxury"
The clincher for me, if it was that close a choice, would be that currently nobody on here is aware of a way to flash out the error codes on a 2.2. They cant be paperclipped. So any issues, you will need a code reader.
Get yourself a 2.6 lad, you know you want to. The v6 is worth it imho.