My evolution was dry yeast, liquid, liquid with a srarter, liquid with a stir plate starter (biggest leap in quality), then repitching from a yeast cake (racking and brewing on same day), then rinsing for about an 8 month period... then I read S Cer's post about pH of water vs beer. Makes perfect sense so I quit rinsing. Lately I've been brewing a variety of things so I've temporarily gone back to a fresh pack and my stir plate.
When I was repitching, I found that the third or fourth batch in a series would seem best. But, there are so many variables in home brewing, and I had been told that tge 3rd or 4th is best, so it could have just been an imagined difference. I am finding now that a fresh starter from a fresh pack is pretty much as good as it gets, plus or minus some tiny variable that homebrewers always debate. I will only be resusing yeast from now on if its a planned out series of beers. Example: a 60/- to an Export to a Heavy, or a Blond to a Tripel to a Quad, or a G Pils to an Oktoberfest to a Bock. Otherwise I'll probably just go with a fresh pitch.
Edit: Forgot where I was going with that. The up side to not reusing yeast is that you can commando dry hop to your hearts content and not worry too much about mucking up your yeast cake.