when i did my first sytem i was planning on having the loop just before the intake of the pump, that way any air could be bled before reaching the pump and making loads of noise...
now tho i would have it at the highest point in the system so it would natuarally bleed teh system
i now have my reservoir mounted on the top of my case just above the psu and the rad mounted at the underside of the top of the case