You usually want to make the biggest multiplication of quantity*rarity.
(1.12 * 2.47) > (1 * 2.61).
As for farming merciless ledge, I would only do it until you can comfortably farm merciless City of Sarn. Give Merveil runs a try. You can pretty quickly get to level 60 just in a1merc, then get 65 with a few runs in city of sarn after a2merc.
Separately, if you're dying, focus on your resists first. Get a bunch of levels, get better gear, and then start switching out gear for MF.