I bought my first St. Croix rod, a entry level Triumph, my son bought a Fenwick HMX (both spinning). Which would be the better rod for throwing top water poppers?

 

Either or. Poppers are a topwater lure, so all that really matters is length, action, and line used. Sensitivity and the actual materials used for this type of rod really wont matter.

you gatta give us the full specs of the rod before we can tell you which is better.

If one rod is shorter than the other, I'd go with that one. With a popper, I am trying to make pinpoint casts to specific spots next to cover like weeds, logs, docks, etc.  A shorter rod helps with casting accuracy.  I use a 6' spinning rod for smaller poppers and 6'4" baitcaster for heavier poppers.

Both are great all around rods, just wait till you go from your SC2 blank triumph, to a sc3 blank or better on a St Croix rod... You'll be in awe...

If you can give us some specs on the rods as far as length, power/action, weight ratings, that should allow us to better help you. 

depends on the model. Get a medium action rod with a lot of tip, to avoid ripping ou the hooks, use mono too.