I think it depends what your going to use the bike for.
Im 5’8.5″ – 5’9″ with a 32″/33″ inseam. (I think fairly long legs ? and short trunk ?)
Generally I like a bike in 17″. Although I have a feeling womens bike might fit me better ? 🙂
I have a scandal 29er in 18″ but I plan to use it as a pure XC machine, maybe even short bits of road/cross. I also wanted some room to possibly put a frame bag one day.
I’ve rode it round the chase and it handled every thing well especially the climbs, but in comparison to some of my other bikes it feels big. Its not so great for jumps/air I think thats a bit the wheels and a bit the size.
If you want more of a pure XC machine I would think about the 18″ but if you want more chuck ability maybe a 16″ ? Although I have to say at 5’9″ I find my 26″ more fun for jumpy type trails (ie llandegla).