I'd go Aurora.
Aurora take more of a hit and is more versatile (can carry a cargo box). Mustang is more streamline and has more agile flight characteristics, but it's not as durable. Starting with an Aurora, you can earn UEC (in game credits) to buy other ships, once the game gets to that point (it's not yet).
Getting the Aurora, if you don't like it after trying it out, you have the ability to buy a CCU (upgrade) to a Mustang (for real money). The CCU thing is just while the game is in development though. That being said, there's no rush, you've got plenty of time before the commercial release.
Just looked at both the Aurora MR and Mustang Alpha starter packs and they're both $45, so you could buy either and if you didn't like it, just 'melt' it and buy the other one with the store credit you get from melting the package.
Getting in and playing the PTU (Universe in the game menu), most people are happy to spawn a ship for you and let you fly it around. There are also free fly weeks/days from time to time which let you try out other ships.
Have fun and stay safe out there!