I use 50# power pro and while I use uni-knots at times I find that the Polomar knot holds better over time. The obvious exception is line joins which are always back to back uni-knots.

Graybar and several other electrical supply stores carry Lineman's Snips. That's what they're called. I've been cutting superbraides all the way upto 200# for 8 years on the same pair and they're sharp as ever. These things will literally make a penny into a corkscrew and then cut paper with no problem (I've also done that with this very pair). They'll cost you about $20 bucks but they last forever. You can cut wound stainless wire with them too. One side of the blade is micro serrarated so they don't slip on the material you trying to cut.