I live in (and run a hotel, les flocons) in le sauze, about 3km above barcelonnette.
For lift riding there is pra loup (bike park good choice of runs), le sauze (2 so so runs, beginner based and cheap lift pass), as well as montclar (probably my favourite), les orres, vars and allos not too far away.
As for non lift riding there are some good marked trails. Some very technical, one long up for one run down! Trails are generally very quiet all the time.
The transubaye is ok as the scenery is excellent. It also finishes by going through some long train tunnels which is interesting but the general trails is predomenetaly fire road dotted with singletrack.
For some info
http://www.ubaye.com/vtt-ubaye-ffc-transubayenne-pistes-descentes-bike-park.html
And a local trails map http://www.ubaye.com/telechargements/brochures/plan-de-poche-VTT.pdf
Routes 10 and 8 are very good.
Hope this helps.
Paul