Stagecoach have got a good long distance fleet, much of it only being a few years old. The regulars on the X51, X55 and X56 are Plaxton Panther LEs, I believe Fife is the only location you'll find those type of buses. All other routes will usually be Plaxton Elites, though some routes such as the X57 and X58 see a mix of both Panther LEs and Elites, and a couple of Panther LEs work early morning runs to Glasgow. It's also not uncommon to see a Panther LE on the 23 north of Perth.
The X52, being a lower priority route that only has two return trips a day, will see pretty much any type of bus, from ALX400s to E200MMCs to E300s to E400s to Panther LEs to Elites, just depends on what is free at Dunfermline depot. The only thing you won't see on that route is a Solo/Solo SR as they don't have a high enough top speed or capacity for an Edinburgh express.
The X37 also doesn't tend to use coaches, it's typically E400s and/or E300s on that route.
You'll also see deckers on the express routes fairly often - early morning workings on the X24/X27 from Glasgow to Dunfermline will sometimes use deckers, usually E400MMCs, and it's pretty common for peak time workings from Dunfermline to Kirkcaldy to use deckers. They usually put deckers on the X55 on rail strike days as well.
Personally, I much prefer Panther LEs to Elites. They're more comfortable, have better aircon and being partially low floor, don't feel anywhere near as cramped as an Elite - and of course are much more friendly to passengers with mobility issues. Plus, they have USB sockets that actually work most of the time, unlike the Elites.
