there isn't really much to separate those two. so go for whatever is cheaper. the Seasonic comes with 3 years extra warranty, according to the Cybenetics test the Leadex III is quieter used on a 230V circuit (which is quite an odd result tbh), at 110V there's no real difference. there's also an ARGB version of the Leadex III
both are decent units, can't go wrong with either