I'm looking at getting a bulk spool of 12 pound line for my casting rods of one of those two based on the reviews. Any recommendations either way?

I've always liked P-Line regardless of the different styles they put out, I've been using their Copoly for a while now and my next baitcaster will have their fluorocarbon either their Tactical or CX. While I have a spool of Seagur, it has yet to be tested. 

I have used both and for me I have had better results with the invisix. It seems to have a little less memory.

Used both and invisix gets the call

I've used both with good results but Invizix would be my choice. Both have good abrasion resistance but like someone else said it seems to have less memory.

The only reason I would pick the CX over the Invizix is I can get a 3000 yd spool of CX for under $50.  The best I can find a 1000 yd spool of Invizix for is about $64.