Getting close to varnish stage, and was just wondering which would be better to use, the Polyurethane or the spar varnish. I am going to use the System three products, since they are local, and have used their epoxy, but just not sure what the difference is. Which is easier to apply, stand up to abuse? I just have no idea at this point, but have used the poly in the past on other projects.

There's a big difference between the two.

Their WR-LPU Topcoat polyurethane is a waterborne finish. I've used the clear and color coats with... shall we say, limited success. It's left a bitter taste in my mouth. It can be really tricky to apply if you're not used to it (especially if you spray it). Changes in ambient temperature and humidity really reek havoc with application. It is crystal clear and imparts no color to the wood. As such it can look "plastic-y". Long tern durability is OK.

Their Spar Urethane appears to be a traditional oil-based marine varnish. I've never used it so I can not comment on it's application or durability. That said, if it's like most other quality spar varnishes it should be easy to brush on and hold up well.