Best looting ship?

In my universe the xenon keep pushing hatikvahs choice and silent witness. I need high energy catalysts really bad but my looters keep dying to Hs and they send through like three Ks and Is. I've tried using scouts but the Hs especially nuke them. I was considering trying an M ship just made fast as possible but should I go for travel speed, boost speed, or cruise speed? Or should I try slower, more tankier scouts?