When it comes to breadth of model range, authenticity of FDE, instrumentation, sounds, and paint schemes, David Maltby's freeware Comets are the standard, in my view. I like the Just Flight model for its gorgeous visual appeal, but the model range is very narrow, and there are a couple of paint/model flaws - and besides, we're talking freeware, so that's a moot point.
By contrast, David Maltby has made it a hobby objective to model almost every (if not indeed every) variant of the Comet, BAC One-Eleven, Trident, and VC-10. The models show a bit of their age ("polygonal" curvature on the wings at the roots, etc) - stuff common from their original FS2002 heritage - but the panels are superb (yes, 2D) and very immersive.
Not a lot of repaints out there because the base packs cover 1 scheme per most of the major period paints. That said, if you log onto CBFSim, there's a thread for each type, where virtually all hull numbers for all the major British operators have been painted and posted - so there's almost no end of Comet fun one could have if you want to go deep....
http://cbfsim.co.uk/cbfs_bb/viewforum.php?f=17&sid=40f96d708583f3a4a06276f4f3f81d7c
I don't have a ton of time on his Comets as the type is just not my cup of tea (I prefer rear-engine airliners a whole lot more) - but having lots of time on his BAC and Trident, I consider these - alongside the AFG Caravelles, my hands-down favourite FS9 portover airliners.
So if you're a hardcore Comet fan, you'll likely really enjoy David's freeware Comets!
Hope that helps,
DL