15” K Lights and 14” K Custom Darks, depending on setting and music.
The 15s for music that is focused more on vocals, songs that might have originated and stayed with an acoustic guitar, that won’t need to get too busy and might need a lower pitch flavored with tawny port to not invade any of the vocal’s sonic territory, and be served well on louder choruses with some open sizzling slosh. Live or recorded. Aimee Mann.
The 14s for pop/funk/rock/soul where some crisp citrus flavored vodka is needed to cut through those guitars and busier patterns, and flourishes, swoops and barks are integral to the genre. Elvis Costello/Earth, Wind & Fire/Gil Scott Heron mashups.
14 was my size for decades. Lately I have been using 13 with no problems, and even have a few sets of 12, which I think are fine. I have done the same with ride cymbals: for decades 21 was the smallest I was willing to use, preferring 24s, but 22s too. Lately I have been using 18, 19 or 20 inch rides. I even have a 17 with a 3-rivet cluster that I use on occasion. I don't use crashes, so those have remained the same size for me: 0 inches
My 14" 60s/70s New Beat works with everything. Hairline fleabite/crack on the top edge made me retire them for jazz combo work... (a hard core drumming son has costed me more than so, when it comes to cymbals...)
My 13" Paiste black label 2002 medium hats are great in smaller combos.
But, with my current band my 16" black label Paiste medium over 16" red label Paiste power crash, is my to go hats. Works as third crash when "needed" and fills up the overall sound with a shimmering wash during guitar solos.
I've played 13's, 14's, and 15's all Zildjian new beats from the 60's and 70's. My preference are the 15's. Love the way they play and sound, but I think it has a lot to do with the style of music you play. I play a verity of stuff from the 60's through the 90's. Stuff from the Stones, The Who, Zeppelin, the Beatles, REM, U2, Black Crows, Stone Temple Pilots, 3 Doors Down, Green Day and the like.
Regular cymbals. Right now I'm using a 50's A over a Ufip Natural Series.
I wouldn't recommend 18's as a do-it-all set. But in the context of a loud rock band with lot's of open hihat, they sit really well in the mix. And the look on the sound guy's face, when you set them up, is priceless
Well from all the responses, I'd say it comes down to trying different sizes, etc. and finding what sounds and feels best to you and works best for the music you play. FWIW, I love my 13" K Custom Dark hats. They work for everything I play and I just never have found any other hats that have tempted me to make a change. If I'm playing a loud gig unmic'd, they can have a hard time cutting through the mix. But I generally don't do that... so all is good.
I like my 13" Sabian AA hats for their quick response & bright sound that isn't overpoweringly loud. However, I'm starting to think about looking for a bit darker sound & will be considering moving up to 15".