Have had both. First was a 6 pot (2.6 manual) last 2 have been 4 pot (2.2's manual and now auto). All Estates
IMO, and I am SURE I will be contradicted on here, I have had a lot less trouble with the 4 pots over the same time period of owning each one.
2.2's can be claimed to be underpowered and less MPG but having never run any of the bigger 6 pot I have found the 2.2's to be the same as the 2.6 if not a little better.
The Manual's were obviously slightly better on MPG and performance than the auto but in todays town traffic, and cruising, I have preferred the auto.
My reading of the posts on here is that the usual problems, cam belts & cover gaskets, sensors, head gaskets, etc.... occur on both 4 pots & 6 pots. Up to you to decide which you would be willing to work on yourself.
I have an Omega because I like the Omega, for it's comfort and more importanly to me it's size. Do not know what I am going to do when I can no longer get one.
I am not an expert as such just letting you know what I have found.
Hope this helps
Phil