Cucumber from TFA is what I found to be most realistic, though it smells like alcohol pre-steeped. Capella's cucumber is a little pasty, but a solid additive. And normally I like Flavour Art's flavors, but their cucumber is really sweet.
Mint easily takes over the Cucumber's light watery flavor so you really have to use low percentages. I found creme de menthe from TFA the closest to what I want because it's creamyness is smoother than regular Spearmint and peppermint (which are too sharp). But this is my subjective palette talking so gotta do what you like ya know.
TFA Koolada is always a solid additive to get that cool feeling in your juice.
I think my latest recipe was TFACucumber at 8% and creme de menthe at 0.5%. I know Coval Vapes uses a pinch of Dill in their cucumber mint.
Do not heat steep mint flavors, they will fade. So I've heard..