EARL
EARL was always a non-starter, both on cost and risk and the SNP were right to dump it before even more money was wasted. The replacement link - a heavy rail station at Cogar interchanging with the new Edinburgh tram line into the airport is a much more sensible solution. I don't know what the costs of this are off-hand but, including the new link from the main Glasgow/Edinburgh line, it will be a fraction of EARL.
Compared to Glasgow, Edinburgh has a much larger spread of direct International services, handles more aircraft movements, greater passenger numbers and vastly more cargo and mail. It is now incontestably Scotland's premier airport and with the new Cogar link connecting it by rail to most of the rest of Scotland, and to North and East England, that position will continue to improve.
Glasgow on the other hand has GARL, which with the best will in the world only makes a very marginal improvement to the airport's connections to the rest of the country. The new M74 extension will help too but I doubt that even together they will get Glasgow back onto an even competitive footing with Edinburgh.