The regular couatl got a whopping +3 LA, which its 9th-level sorcerer casting probably had something to do with. The psionic version changes barely anything: the only difference is a change in SLAs.
Where the regular couatl had the detect [alignments], detect thought, invisibility and plane shift at-will, the psionic variant instead has a number of PLAs. These are at-will Aura Sight, Cloud Mind, Detect Psionics and Read Thoughts, and 3/day Mental Barrier, Psionic Plane Shift and Thought Shield.
Even though the regular couatl has some tricks the psionic one can't match (at-will plane shift), I feel like the psionic version comes out on top in the end. +3 LA for those too, because more than that would be ridiculous even for this monster.
I could also imagine some people would advocate for +2 LA on both variants, or +2 on the regular one and +3 for this, and look forward to seeing those opinions.