I would prefer a non-spell-based psionics system.
Spells are discrete things. You cast fireball, and you get a 20-foot-radius ball of fire somewhere far away doing X amount of damage. You cast haste, and the target moves faster and can do more stuff. It is trivial to create a character who can do both of these things.
Psionics, at least to me, lean more on sci-fi and superhero tropes. In those, it is more common to have one (or rarely multiple) core power(s) that can be expressed in different ways. Xavier is a telepath. He can communicate telepathically, read minds, create mental blasts, create mental illusions, project astrally, and use his telepathy in a number of other ways. In the OG Marvel RPG, this was expressed as having the Telepathy power and a number of "Power stunts" based on that power. But he can't move things with his mind, or see the future, or walk through walls, or heal his legs.
My preference would be for a psionics system that used that as a core idea. The closest was 2e, where psionicists started out with a single discipline (telepathy, clairsentience, psychoportation, psychokinesis, or psychometabolism – I don't recall if you could take metapsionics as a primary discipline, but it would likely not have been a good idea even if you could). Even then you could branch out, but one discipline would always be primary.
Now, 2e psionics were far from perfect. The telepathy powers were too punishing for non-psionics, and the system was mostly too flat (1st level psychoporters could have, and probably would have, Teleport as a power – far shorter range than the spell, but still). But deep down, it's what I think of as being "right" for D&D psionics. Perhaps because that's where I started, but also because of this approach of powers being different expressions of a core discipline.