What are ROH's best matches in these categories, in your opinion?
Best chain wrestling match
Best steel cage match
Best ladder match
Best hardcore match
Best powerhouse match
Best highflying match
I'll give you my list based on what I've actually seen and what comes to mind instantly.
Chain Wrestling = Bryan Danielson vs. Nigel McGuinness from Weekend of Champions Night 2 or Bryan Danielson vs. Claudio Castagnoli from Northern Navigation, or really just anything involving Danielson, as said before.
Steel Cage Match = ROH vs. CZW from Death Before Dishonor IV, which is Cage of Death. Brutality and entertainment at its finest with an awesome feud to back it up. But if you're looking for a traditional steel cage match I'd say BJ Whitmer vs. Jimmy Jacobs from Supercard of Honor II. Awesome stuff.
Ladder Match = Kevin Steen & El Generico vs. The Briscoes from Man Up. One of my all time favorite ROH matches. Crazy shit all the way through.
Hardcore Match = ROH vs. CZW Street Fight from the 100th Show or CM Punk & Ace Steel vs. BJ Whitmer & Dan Maff Chicago Street Fight from Death Before Dishonor II Night 2.
Powerhouse Match = Joe vs. Kobashi. Two more I'd throw out is Morishima vs. Shingo from Good Times, Great Memories and Morishima vs. Brent Albright from Death Before Dishonor V Night 2
Highflying Match = Dragon Gate 6 man from Supercard of Honor