I love them both! I would use
Jason if it weren't the name of my best friend's older brother (who I see all the time). I'm thinking about using
Justin! I also like
Justus. I love the meanings of both of them. I think their gorgeous meanings trump how common they are. Besides,
Jason and
Justin are rare gems compared to ubiquitous names such as
James,
William,
Michael,
Alexander, etc.
Jason immediately brings to mind the story of the Golden Fleece, and
Justin brings to mind both the very good-looking
Justin Trudeau and the brave, heroic rat from "Mrs. Frisby and the Rats of NIMH". He's one of my favourite literary characters, so... to me, it really is a wonderful association.
As for combos, hmmmmm...
Jason TheodoreJason CasimirJason BenedictJason DashiellJason CharlesJason EmmanuelJason LeanderJason MatthiasJason NathanielJason Rainier
Justin BonifaceJustin DominicJustin FredericJustin GabrielJustin LeopoldJustin OlivierJustin Pierre James Justin ThierryJustin ValeriJustin Peregrine