I don't think it's humanly possible to feel 'most like yourself' at all times. However I could tell you where I don't feel like myself, I don't feel like myself in formal occasions. I have a crowd problem, I hate it. I try so hard to avoid a crowd that I end up feeling exhausted and angry.
I don't feel like myself when I am in in an unfamiliar set up, I cannot stand not knowing. I hate it with a vengeance. I need to know things and I feel very uncomfortable otherwise.
I'm not myself when I feel like I need to hide. After being in denial for years because people told me it was impossible, I was finally convinced that I'm a textbook introvert. I'm good with people and I have decent people skills, but I tire quite easily, I cannot socialise and it pisses me off when I am expected to.
I feel most like myself on my own. Give me some place to keep quiet in, I will love it. I will stay indoors, i will go out walking, I will sleep, eat and make merry all by myself, without the slightest need for a "social life". Even on the occasions that I go out, I like quiet, quaint spots. I 'm not for the noise. I'm not myself in a night club, I don't fit in and I won't even try. If I'm dancing, it's to my own tune. I don't care about anything else. I like that small bubble that I build around myself and I'll live in it.
The question isn't really "when or where". It should rather be what makes you feel like yourself. What make me feel like myself is having freedom. Where I can be myself, is where I have the freedom.