wow man. that's a pretty vague question. You need to input a few other things for that answer... how wide/thick is the board? what kind of tail? what fin set up are you looking at? are you looking for a gun, semi/minisemi gun, step up, thruster every day board, pod, fish, minimal, velo simms, or any other alternative kinda board? Then the questions begin of what kind of wave are you riding? Beachbreak? Pointbreak? Reef Break?
I mean I have quite a few boards and they vary from a 5'6 velo simms up to a 7'0 CI MSG (mini-semi gun). My normal everyday board is an 5'11 MC Bonzer 5 fin octafish, my thruster is a 6'2 Zamora, and my step up is a 6'4 MC 5 fin "Shelter" bonzer. I'm 5'11 X 190. those are the three boards I ride most often but I also have a dozen others that vary greatly size wise depending on the shape/design of the board and what it's intentions are for.
I know this isn't a direct answer, but you need to give more input for a better & more concise answer.
6'1" 20" wide 2" 3/8" thick IF you only go out waist to 2x head
if you are always stuck with crap, weak gutless surf get a 5'10" or 6' quad fish width round 22" wide same thickness. that shape and design will surf anything, really maneuverable (will take a while to get used to tho)
p.s thrusters/squash tails really only work in chest + surf (sure you can ride it in waist high but ur not doing much)
i have 7 boards and like someone pointed out it all depends on the conditions, dont limit urself by only surfing one board and only having like 2 or 3 others u never use.
im 6 2 175 i ride a 6 2, 18 1/2, 2 1/4 santa cruz standard squash tail for eveyday here in jersey beach break. i think you know by know what feels right under your feet dont look so much into oppions exp since you know what you doin Inkn.