Good question. I really believe it depends on your intentions further down the line. If - as you say - commercial is in your future, then I'd go down the glass route. That way you'll become comfortable with a type of instrumentation that you will be using later on.
If, OTOH, you will continue as PPL and rent the usual rustbuckets
that fly around Europe, then the steam gauges are perhaps the better idea. That said, at least in the US an increasing number of rental a/c also come with glass, so even that point may well be moot.
Personally, I'd go for the glass, as it's the way instrumentation is evolving and I'm sure it's a lot easier to get used to the 'steam driven' gauges coming from a glass cockpit, then the other way round.
One - small - word of warning, though: your profile doesn't say where you are based and which license you are training for. Should this by any chance be an FAA license in the US, then be aware that you will have to demonstrate knowledge of ALL a/c systems on the checkride - with a glass cockpit, that may well be a handful..... (disregard this para - didn't see your location as 'Sussex' when writing)
PS: I'm sure there will be all sort of people on here in a second going on about 'looking out the window', 'stopwatch and paper map', etc. Don't worry about them - the future is electronic.