Yea, TOW The Flashback was the episode that really made me really appreciate Chandler/Rachel in a romantic context, but I saw TOW The Cheesecakes before I watched that (I came into the show late), and I loved the friendly dynamic and chemistry they had. I didn't know they had kissed in earlier episodes, so it was just a crackship of mine that I didn't take seriously because of Chandler/Monica and Ross/Rachel. They're my two favorite characters, so that played a part in my love for them too. I just loved how FUNNY they were together, and for a sitcom, you want that. Then I saw TOW The Stripper Cries, and it went from crackship to actual-ship-even-though-I-knew-it-would-never-happen.
I actually think I read once that the writers were planning on putting them together, then decided against it? Or they were part of the original plan when they created the show?