Engine Oil

In total confusion over engine oil, for my 2006 Clio 197.

Service booked at weekend (Saturday) - need to purchase some oil prior to this, what grade do I need, read the technical information but I don't understand.

0W/40 or 5W/40

Where is best place to purchase it from? Best make from experience?

Thanks in advance, just after some people who know with time running out on me.
 
I recently bought 6ltr of ELF oil from Renault and the price was really fair tbh, worth a shout. You can go in to your delearship and buy it there and then.