Second the hatamoto as the most iconic draconis combine mech. The no-daichi I like more, but hatamoto's are on so many book covers for a reason.
The lyran fafnir from the field manuals or axeman cause of the cartoon.
Marik the Perseus from the field manuals or wraith
Liao the pillager or emperor kinda defined the "new" liao jumpy boys ad poster mechs especially with st ives.
Davion the templar is probably the most poster worthy.
The jade falcon cougar saw a lot of video game appearances and that fire falcon/black lanner/cougar shape is the new look of the clan in 3058 Once partial wings are a thing those wing mechs take over the new styling for the clan for sure.
Wolf has so many "wolf" mechs that are variants of the timberwolf, that none really shine as their own unique creations. Savage wolf may be cool but I still just see timberwolf.
Ghost bear after the Kodiak they get lots of bear themed mechs but like clan wolf none outshine the Kodiak even if they are stronger/better balanced mechs.
Comstar im a sucker for the raijin. The shootist is interesting but not as striking and the tessen is too techy/undergunned to be a poser child. Like if the tessen was the mech in the recruitment poster for the comguards id take my chances with WOB.
Wob, not counting the celestial series with their striking looks, the Toyama just hits right for me. You can definately put that mech on a book cover to send a message.