I think if you are trying to match ANYWHERE, you probably have a better shot with IM due to the fact there are many, many more community-based programs...and if you aren't really interested in neuro, they'll figure it out during your interview and you likely won't match there. Fit and interest are key to neuro interviews.
However, the competitiveness in high-tier programs is probably similar between the two fields, in the sense that you gotta have a great application on paper (scores, LORs, etc.) to even be afforded an interview.