The question is simple what is yopur favorite weapon in 40k? At Range and in Close Combat.
For me its...
Range: Flamer- its doesn't need to roll to hit and usually covers alot of enemies. It also ignores cover saves which are everywhere in 5th.
Close Combat: Thunderhammer- its a powerfist that if...IF your opponents survives the hit he strikes last in close combat as he is stunned.