I like Reta for sure. It's been life changing, so far. As for non-GLP peptides, I'm not sure because I haven't tried them all yet.

In the running would be Epitalon and NA Semax. Mots-C really kicked my ass today in a good way, but I may save that one for when I need to fight bears or jump from building to building. I thought SS-31 was a dud, feels-wise, but if it prepared me for Mots-C and the blast I got today, then it certainly did it's job. KPV is a keeper, so is TA-1 and Selank.
So I guess haven't found one that I would say never again. I do think if you are older, you feel them more because they are designed optimize aspects of your metabolism, brain signaling pathways and immune system. If you don't have that damage (yet), or deficiency, you may not feel the impact. You can't optimize an already optimal system.