I'm with Cumbernauld Flying Centre, and find them very good. I do only have around 20-25 hours, but so far I've been satisfied.
The frequency of my lessons really don't warrant a comment on a/c availability - I book a month in advance, and they are always available.
I have had a mixture of instructors, can't fault any of them, largely consistent.
I'm on 2 aircraft at the moment, with most of my time on the Katana, but trying out the Robin. I prefer the Robin, so I'm hoping to move onto that fulltime, but as they only have one, I suspect availability on that particular A/C will be limited.
Give them a try.