I've been doing ELISAs for several years as a grad student, and I've always used a linear best fit line for my standard curve. I'm currently trying to troubleshoot an ELISA that someone else has done, and noticed that he was using a 4-parameter standard curve. When I do a linear line on all of his data, I get r-squared values that are a bit lower than his 4-parameter best fit lines.
Is a 4-parameter best fit line OK to use? I've always been told to use a linear line, but when I use a linear line on his raw data, I get slightly smaller r-squared values (.9978 vs. .9789 for example).