I tried to use two OpenSSL forks yesterday with curl. I built both from source first (of course, as I wanted the latest and greatest) an interesting thing in itself since both projects have modified the original build system so they're now three different ways.
libressl 2.0.0 installed and built flawlessly with curl and I've pushed a change that shows LibreSSL instead of OpenSSL when doing curl -V etc.
boringssl didn't compile from git until I had manually fixed a minor nit, and then it has no "make install" target at all so I had manually copy the libs and header files to a place suitable for curl's configure to detect. Then the curl build failed because boringssl isn't API compatiable with some of the really old DES stuff - code we use for NTLM. I asked Adam Langley about it and he told me that calling code using DES "needs a tweak" - but I haven't yet walked down that road so I don't know how much of a nuisance that actually is or isn't.
Summary: as an openssl replacement, libressl wins this round over boringssl with 3 - 0.