I know little about Glasgow College of Nautical Studies, except that they have only 4 instructors (I applied for one of the jobs when SFT went bust). Don't really hear much about them. Ask them about class sizes, and look over their notes and compare to other schools.
To add to what FFF is saying EasyJet fly from Glasgow to Bristol (I know, I missed the flight when going for the interview and a lorry squished my car). Book early it is the cheapest way down.
I think Ryan Air now fly down here to Bournemouth from Prestwick if you want to study at either of the distance-learning schools down here (GTS and my employer, BCFT), and accomodation is again cheap.
Not sure about convenient transport to any of the others.