If you're buying DRY/RAW *DENIM* then ideally you should buy a size up, as on first wash the denim shrinks around 2inches depending on the brand, however, as they are worn (for example over a period of months with no washes) the denim stretches back out to the original size, but as soon as it's washed again it will shrink back down to the 2inches below tagged size.
It depends whether you wash your denim frequently (sounds like a silly question, but many denim 'headz' will wear their raw/dry denim for maybe a year without washing, with only one cold wash then airing/dry cleaning to keep clean) they do this because then the indigo fades in all the hard wearing places (bum, pockets, creases, 'honeycombs' behind knees etc) and once they do get washed (e.g after a year) the indigo fades significantly in all these places creating beautiful naturally 'worn' denim, full of actual character rather than buying jeans with a wash already (e.g fades and holes) ..you tend to find it doesn't look very natual and all the fading is wrong.
Sorry to waffle on, I love clothing, jeans and trainers are my favourite subjects8) if you want my opinion, if getting maharishi, definately go for raw/dry denim (which is when it hasn't been washed at all, dark blue indigo colour) you may find they're quite stiff,especially after the first wash, but the more you wear them the softer they'll go..) I have a three year old pair of evisu's which started off raw, they're now faded beautifully around the pockets and stitching, the guls are gradually fading too (which I'm happy about, evisu is quality denim but the label has been dragged through the dirt by fakes, the gul is becoming the new louis voitton pattern..) If you want some pics, PM me.
Let me know what you choose!
Ooh also, if possible, get your denim with selvedge, not only does it look waaay better if turned up, but the way in which its loomed is much better
selvedge: