Well, me being a petrol head non diesel liker, I would say instantly "buy the petrol" but then depending on which petrol. A 2.4 without i isn't worth the hassle. It is greedy, a slug and basically produces far too little power. The 2.0l is the more modern construction with a more up to date design (though still rather old, late 90ies/early 2k).
The 2.0d can be cheaper, depending on which version you get. Euro 3 (without DPF) or Euro 4 (with DPF - though there are some without, a friend has a 2007 C30 2.0d with Euro 4 and no DPF, so look right
). If with DPF, it will get very costy. Every 3 years (or 37.500 miles, what ever comes first) new Eloys additive and every 6 years (or 75.000 miles, what ever comes first) new DPF and Eloys. These cost cost cost and again cost.
So unless you find a 2.0d without DPF, I wouldn't get one. They get too dear to run, though they save on fuel costs.