[jamesash]

It's pick your poison, like choosing a startup vs BigCorp. My observations pertain to organic chemistry specifically, I'm less familiar with other fields.

With an assistant prof you will be asked to do unreasonably long hours on ideas that haven't been fully validated, but you get a lot of face-time with the PI (for better or worse) and have a chance to get on the ground floor of a potentially great research program. Your boss has a lot more invested in your success because their career depends more on you. It can be exciting.

With a more established prof you are more likely be plugged into the n-th iteration of an established research program. You're more expendable because the prof has more options to hire your replacement; you can get lost in the crowd; the prof won't be in the lab as much (travel, service responsibilities) so it's more sink or swim. Lots can go wrong in this environment. As the group gets larger, internal politics can create frictions, especially if the supervisor is away a lot.

I see A) as better than B) but that is just me.

[BeetleB]

Yeah, it will vary with the discipline/major and possibly also the rank of the university. My point was that from what I've seen, the startup vs BigCorp dichotomy wasn't as clear cut as you describe. Also, there is the third category: Small business. Few grad students, and relatively low pressure.

[jamesash]

>Also, there is the third category: Small business. Few grad students, and relatively low pressure.

These can be the saddest cases in my opinion. Lower downside, but lower upside too. You work your butt off and knock the ball out of the park with your project: who notices? A few experts, in a very narrow field, may recognize the significance of what you've done. Can be lonely.