I'm looking to change my bike crankset and was looking at Sram S100 or Sugino Messenger however I'm not sure about wich spindle length should fit my frame.
Manufacturer specify that frame uses 111mm (ISO) should I go for a larger spindle or shorter one? I need you advise on this.

Spindle length is determined by the crank rather than by the bb shell which is almost always 68mm.

Ok so Truvativ Power Spline bottom bracket the one that fits Sram S100 crankset came in 113mm, 118, 108 and even 73mm they're all 68mm wich one should I buy?

What kind of frame are you riding? Your frame probably has a 68mm BB shell. The spindle length suggested for a Sram S100 crankset in a 68mm BB shell is 113mm.

an Eighthinch Scrambler and yes BB shell is 68mm

The Scrambler has a 68mm BB shell so you need a 113mm bottom bracket.

Thanks a lot