Welcome to Flyertalk Neil

Your question is not easily answered, in part because the grass always seems greener just over the horizon. When you get there you realise that, well, it's just the same grass.

Example 1 of many ideas: Since you're based in Glasgow, many of your flights are going to involve a stop somewhere. Now that may speak for BA, but of course you could fly LH and connect through FRA or MUC internationally. LH is slowly introducing a premium economy product, but I can't tell you that much about it yet. But have a look at the LH forum and you'll see plenty of people complaining about the Miles and More programme. Another consideration is that LH flights that do not go into either of the hubs are actually operated by Germanwings.

And so it goes on....what would be your usual routes, and which carriers would you most likely fly (considering who offers Y+)? Skyteam is pretty rubbish overall, and I think your choice may come down to the best, suboptimal, solution (ie sticking it out with BA).

Moderators may wish to consider moving this to the BA forum, where you'll get more contextualised input.