Choosing a next ship

So i'm totally new to Elite Dangerous and did some research online. Ive seen a lot of people say to save up for the cobra mk3 as your very first bought ship but as my final mission i earned around 200k creds. I've got around 500k now. Now my question is do i actually buy that or do i immediately get something more expensive but better like the diamondback scout or the viper mk4? I mainly do cargo missions so far like bootlegs and cargo transports. So something that has more cargo space would fit but i can't wait to hear more advice. Thank you in advance!