I'm not certain about reliability - quite a few of them have small reliability problems while others are very solid. But can give experience from a driving point of view, since I drive a wide range of cars in my work.
The old, original 90bhp and 110bhp non-PD cars (~pre 2000) are solid performers at low speed, great throttle response, very agricultural in noise but quite charming as well. They moved Passat, Golf and A4 along quite smartly. Last year I was driving one with 230,000 miles - see Reader's cars forum.
The replacement 100,115,130 and 150 bhp PD engines are a lot more modern in terms of the powerband, and have a great slug of mid range torque. Between them, though, they do not wildly different from each other in their performance. They each seem to pull similarly at lower engine speeds. The 150 does not feel much faster than the 115, in my experience, although the figures confirm that it is. I'm sure it is faster when revved out to the redline, but it still feels terrible when driven like this - revving the nuts off a diesel always feels unsatisfying. In 130bhp form I felt that this engine moves an A4 or A6 Audi surprisingly smartly.
The 2.0 tdi engine with 138bhp was another hit - great performance in small cars like the A3; it punches above its weight. I haven't driven the 170bhp version of this, but wouldn't be surprised if it felt only a bit quicker, or no quicker at all. Put this 2.0 tdi into a bigger car like a Golf plus or a Passat and it does blunt the performance quite a lot and it's no longer all that exciting, but in an A3 sized car it does a really good job.
Then came the common rail technology 2.0 tdi. This is noticeably much quieter and smoother than the earlier 2.0 engines. But the performance has not changed. It is delivered more smoothly across the rev range and is more petrol like but I can't help feel that it's lost a bit of its excitement at the same time. However I've only sampled this in larger cars - A4 and Passat, both of which it moved along acceptably but without excitement.
Probably as diesels go these are the best I've tried. The Fabia vRS is speedy in a straight line but a cruiser not a handler.
Their economy has not particularly improved over the years but power and smoothness have, a great deal.

My Audi A6 1.9TDI (130) has just passed 160,000 miles and sailed through its 5th MOT without any problems. All it gets is a service once a year and so far so good.

Please don't get a MK4 Golf hateful things.

I've just spent driving around for three hours. Hatefuls cars.

The curse of modern cars, unfortunately.

Just about every diesels and many petrols have dual mass flywheels which break up and are horrendously expensive to replace - it's certainly not limited to VAG.

Or perhaps a Toyota Prius

Round trip, my 330 is on 160k, and not overly keen on LPG after my old mans Disco gave endless LPG problems.

I might get shouted down for saying this as there seem to be more "dieselheads" on here now. But I would suggest running your BMW 330i for a couple of months and see how you get on fuel wise. My 325i easily achieves 36mpg on a 40 mile run. When you work out the additional cost of fuel and the cost to change you may actually end up worse off. I've had a PD160 (Ibiza Cupra) and two PD140's (A3 & A4) and I never got more than 45mpg combined from them.

It was missing like a sod, he took to a number of both landrover and LPG specialist, none of which could find the issue.

To be fair, although I like land rovers, they are really not built very well at all.

So is LPG a big no no?

Cricky, this is a bloody nightmare, luck of the drawer I suppose

haha, bugga off!