The only place I would use the uni to uni is where your braid meets the mono backing on your reels. For leader to mainline knots you should be using the Bristol Knot or the Yucatan Knot. Tuna fishermen are known to love the Yucatan Knot, that should tell you something.

I catfish for the big ones and I prefer the Bristol or Yucatan...you have to tie either a Spider hitch or double overhand surgeon's knot in the main line and then attach your leader to the loop you created. For attaching bass lures to the leader, try the Tuna Knot...it's great.