The Titan UK trades are better quality reproductions than the IDW ones. They are a little random though sometimes including stories that don't thematically fit. The first few told the Galvatron story based around the 'epics' (Target 2006, Wanted Galvatron, Legacy of Unicron, Space Pirates, Time Wars), and the later ones went back and picked up others on a similar themes (Dinobot Hunt, Second Generation)
Many of the black and white stories were reprinted in digest size, but again it was a bit random.
From both some tales fell through the cracks. Particularly early ones like Enemy Within and Annual Stories like There Shall Come A Leader.
Titan's reprints are complete for Marvel US except for (IIRC) #43 Big Broadcast of 2006 & the limited series of the Movie, the Universe series and backups, the two GIJoe crossovers, and I think the Ghosts story from G2 #2
The UK stories take place in between the US issues, which makes me wonder when the new trade lists the US creators could this be the most comprehensive reprinting yet.