I only look at gear - their melds don't matter because they add so little that any issues are going to be down to actual gameplay problems or garbage gear rather than what trash they have melded.

i do believe people should avoid slotting BOTH Direct Hit Rate and Critical Hit. i would say the only exception being the gear doesn't have room for any other stat(s) you may like/want. otherwise, i believe it would be better to capitalize on one or the other.
If, after melding any spd that you need to hit a breakpoint, a piece is capped on crit, you meld dhit. If it's capped on dhit, you meld crit. If you can get both capped then you meld for that, and if there's room left, you meld det. It really doesn't matter so long as you're maximising your melds if you're trying to be optimal (for what little it gets you).