Legionary Loadout for Raiders

This has been answered in somewhat in places, but I wanted to get a better feel for why people chose X or Y. I'm building my first 40k army as Renegade Raiders, and am conflicted about Legionary loadouts. Per each 5 man unit should I go 2x heavy melee and the rest astartes chainsword OR swap one of the chainswords for a lascannon or reaper autocannon. I'll likely have at least 3x 5 man units, and I've seen bunch of lists with either a Lascannon guy or autocannon guy. I've also seen a ton of people just recommend all melee and to forget about the heavy ranged weapon. Do you guys generally take either an auto cannon or las cannon, or just all melee? Do the heavy guns give me much more flexibility?