If you get the 1.8 TDCi it doesnt have a DPF, for that matter I cant recall if both the 2.0 and 2.2 both have the DPF, but you will always get more grunt outa the diesel...
The 2.0 petrol is still a very good engine overall!
Later (Mondeo mk4) TDCI 1.8s have DPFs, (yours is a 2007, by 2010 they are probably all factory DPF equipped)
As far as im aware all Mk4 Mondeo 2.0 & 2.2s with the PSA engine have factory fitted DPFs
The OP is accustomed to having a quick car, and the bigger- engined/ more powerful Mondeos may be more suitable for him, often, if you are used to running/ owning a more powerful car, "downsizing" to a less powerful/ slower car can be a big dissapointment and can suck the joy out of motoring - An Astra VXR is quite a fast car, its about the equivelant to a Focus ST - even a stock one almost as quick cross country as my Mondeo (don't ask how i know this )
There is always the 2.5T - fast car, nice to drive, shame about the brakes and the MPG
Astra VXR (05-10) 236HP 6.2 SECS 0-62, 152MPH
Mondeo mk4 2.0L (duratec) 145hp 9.6SECS 130MPH
there are 3 different 2L petrol engines, in the mk4, the "old nail" of the 145/150Hp NA duratec, and the 203 and 240Ps ecoboost turbocharged engines, far better/ more powerful, the car in the OPs ad, has the "old nail" (its the same engine that was in the mk3)