In this scenario, you have to look at what will serve you best. Better pay for a longer period,or less pay on a temp contract but having a manager you like? It looks like a no-brainer when you put it like that, doesn't it!
Take the job as a driver's mate, and write Argos a kind letter thanking them for the opportunity,however you have been offered an alternate position that better serves your requirements at this time. Neither job is set to offer you 'nothing', because they both offer different alternatives for experience and skill improvement, and either will look fab on your CV. If you've only been at Argos a month or so, it's probably not even worth mentioning on a CV – you'd spend more time explaining it to future employers.