I was about to start similar topic myself. Here’s my experience. I have Walthers latest #10 switches. They are OK, all metal and DCC-friendly. But the frog is a bit too wide so car wheel dives in it a bit. Then I found Atlas Mark 4 turnouts and let me tell you I was pleasently surprised! So much that I no longer buy Walthers turnouts. All of my layout now uses Atlas Mark 4 #8. They look great, frog is better, they are DCC friendly and cars go over the frog with less wobble. I hope Atlas will be making other type switches in this series.
The difference I noticed was where you power the frog. On the Mark III it is inside the rails of the track next to the frog. On the Mark IV it is on the outside of the rails which makes soldering a power wire to it a breeze.