Mark VIII: The Mark VIII cruiser served the Legion from Action 386 through 392, again with minor design changes along the way.
Mark IX: Cruisers of the Mark IX design appeared in Superboy 172 - 183, but this design was no more satisfactory than the Mark VIII.
Mark 494: In LSH (v. 2) 285, the Legion received 5 Mark 494 cruisers from Nullport. The Mark 494 was a redesign of the Mark X, more compact and with better euqipment.
Mark X: With the advent of the Mark X cruiser, the Legion finally had a state-of-the-art fleet that was a worthy successor to the Mark III/Mark VI design. Fully equipped, spacious, and striking in design, the Mark X served the Legion from Superboy 193 thru LSH (v. 2) 285.
Mark XI: The Mark XI cruiser, which replaced the Mark 494 in LSH (v. 2) 307, is basically the same design used by the Legion today. More compact and more heavily-shielded than the Mark X or Mark 494, the Mark XI's modular design facilitates mass production, allowing for easy repair and replacement of damaged vessels. As hard as the Legion is on its cruisers, this is a definite bonus!
Dork Note: What the LSH use today I have no idea. The history has been reworked and reworked that I don't even know what's what with that part of the DCU.