I previously worked at two startups and founded one and currently work at Google.
I'm going to be weird and say do the startup. This has everything to do with your particular situation; you've already worked at a big company, you'd be joining Google in a sales capacity instead of an engineering capacity, and you like and trust the founders of the startup.
In general you want to optimize for learning experiences. You can get certain learning experiences at Google that you can't anywhere else - but the difference is much less in sales (where things may run a bit more smoothly, you may be introduced to some interesting systems) than in engineering (where there's certain knowledge that you just can't get anywhere other than Google). You've already done the big company thing; Google will have better perks than Shell, it may pay better, but it's not going to be fundamentally different.
BizDev in a startup, however, will expose you to all sorts of challenges that you don't face in a big company. In a startup, everything is an uphill climb; people have never heard of you, and so you need to make them hear of you. And you'll learn a ton in the process.
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I previously worked at two startups and founded one and currently work at Google.
I'm going to be weird and say do the startup. This has everything to do with your particular situation; you've already worked at a big company, you'd be joining Google in a sales capacity instead of an engineering capacity, and you like and trust the founders of the startup.
In general you want to optimize for learning experiences. You can get certain learning experiences at Google that you can't anywhere else - but the difference is much less in sales (where things may run a bit more smoothly, you may be introduced to some interesting systems) than in engineering (where there's certain knowledge that you just can't get anywhere other than Google). You've already done the big company thing; Google will have better perks than Shell, it may pay better, but it's not going to be fundamentally different.
BizDev in a startup, however, will expose you to all sorts of challenges that you don't face in a big company. In a startup, everything is an uphill climb; people have never heard of you, and so you need to make them hear of you. And you'll learn a ton in the process.