Different answers, which is the interesting part of the question.

Business: firmware. Best margin thing we do and the hardest to copy. Plenty of
people have taken a run at serious third party mining firmware and there are two
left standing. It's also the control layer, so if I keep firmware I can rebuild
most of the rest of the stack on top of it later. Keep the pool and I can't
rebuild firmware.

Personal, money no object: the pool. Which is the worst business of the bunch.
Fees only move one direction, customers switch over a basis point, and what we add
over the next pool is close to nothing on a spreadsheet. I'd still keep it.
Running a pool means being in the chain instead of selling picks to people who
are. I don't want to be a vendor to Bitcoin. The pool is also where I learn
things. Every problem in mining shows up in pool logs before it shows up anywhere
else.

Ask me this in 2019 and I'd have given the same two answers and been wrong about
the business half, so grade accordingly.