LPG every time.
I've been using it in cars for years and have never had an LPG system fail on me yet. I do change the LPG filter every 10,000 miles or so, and drian the heavy ends from the reducer at the same time, but thats it. An LPG filter is about £8, draining the heavy ends involves undoing a screw, and doing it back up again. That's all you have to do for regular servicing. There are conversion costs, but they're re-coupable in a year or so depending on milage. Do it yourself and you're all done for £1000.
Insurance isn't an issue, you have to tell them, but as it's not a "performance upgrade" it doesn't have any effect on your premium price.
LPG does burn hotter, but so long as you keep your cooling system in good shape you shouldn't get any problems from that.
Also because LPG burns cleaner than Petrol, you oil stays in better shape for longer, I wouldn't recommend extending the service intervals, but over the years your engine will get cleaner inside than when it was running only on Petrol.
I've been looking in to this slipped liner problem all over the internet over the last month or so, and there doesn't seem to be any evidence that LPG blocks fail any more than Petrol ones. It seems to be very random. The Rover V8 engine converts well, with many people having done 10's of thousands of miles on LPG with no problem at all.
You might worry about driving along in a potential gas explosion, but the fuel systems are much safer than petrol. Cut off valves at both ends of the fuel pipe, a strong pressure vessel rather than a tank made from mild steel, and a fuel that if leaking due to impact would boil off and dissipate into the atmosphere rather than form a brooding puddle under your car. I think it's very safe.
I also should admit to understanding the Petrol engine better than the diesel engine, so I'm happier working on one, that combined with longer service intervals over a diesel, smoother engine, and less smelly fuel is enough for me.