I agree with lots of what's already been said: I like Chioggia leaves, too.
Sea beet leaves are good in a stir-fry and if you keep letting your chard self-seed, it practically reverts to sea beet!
I do like baby spinach leaves in a salad, but my current leaves are New Zealand spinach, grown in a florist's bucket.
The other one that people might like to try is the leaf beet variety Erbette. It's more tender, after cooking, than other beet leaves I've tried and yet easy to grow (at least, in spring, when I tried it) and large-leaved, so easy to harvest and prepare.
Spudbash :)