I'm on an SSD and space is an issue. The MacTeX distribution is over 2GB. BasicTeX seems to be too limiting to be useful to me, unfortunately.
BasicTeX is MacTex's little brother. Initially you will miss a number of packages but it is very easy to add these later using the package manager Tex Live Utility to arrive at the distribution that fits your needs.
'A lightweight distribution' is one of those questions that is hard to answer as one persons idea of 'lightweight' does not necessarily agree with another's!
The question mentions BasicTeX, which is very much a minimal approach. There are a few things that can be done to bridge the gap between BasicTeX and MacTeX. First, you could install BasicTeX and then add only what you need. That of course might be tedious if you need quite a bit. A second approach, if space allows, is first to install MacTeX and then to remove what you do not need, using the TeX Live manager. An obvious place to look there is the documentation tree: there is a lot of documentation in a TeX distribution, and much of it may not be wanted. Finally, you could install TeX Live directly, rather than using the MacTeX 'wrapper'. This brings with it the option to determine which parts of TeX Live are installed (somewhere in the advanced options).