The sad truth is that story mode Chopper and all of his five evolution suck big time, and are generally good only for socketing more useful versions of Chopper like Monster Chopper or some RRs. If you are just starting and miss most units, Tony Tony Chopper Brain Point or Tony Tony Chopper Guard Point have some marginal uses, both are however replaceable by better units.
Tony Tony Chopper Heavy Point is rumored to have gotten another evolution stage on JPN. This means he may be the optimal evolution choice. Of course, it is possible all of them will get another evolution choice one day. For today, however, they all still suck.