Floor joist nogins

[i_am_fubar]

I've ripped up the ground floor loo's floor, made from 38x98mm timber and need to prep it for tiles. I know I need to add nogins, but which sort of timber is best for it? My options seem to be:
'Sawn treated softwood'
'Planed Square-Edged Timber'
'Kiln dried'
'Studwork'

Are there any pro's/con's for these timbers?

Cheers.

 

[noseall]

any timber will do for nog's provided it is not excessively wet and that it is 'man' enough for the job.

the finish is irrelevant, so if cost is a factor then rough sawn would be ok.

 

[i_am_fubar]

Ah, ok. I was just wondering if it needed to be treated. But I guess its out hte weather.