Any tips on selecting one?
In general, as a patent attorney who's worked both in large international law firms and in a smaller firm (patent boutiques) that deals just with patent prosecution, my general advice would be to try and find a good patent boutique. In general the quality of the work will probably be about the same and the patent boutique will probably charge you less money.
It’s a video from a meetup, by the principal of a design firm, about the importance of using legal counsel.