I'm 27 and have been contributing to a 401k through work and then placing the remaining in a taxable Vanguard account (both accounts are 100% in VTSAX). If i'm understanding the other posts correctly, my order of allocation should be first max out 401k, then max out Roth or Traditional IRA (any reccos on which?) and then put remaining in a taxable account. Is this correct?
It can be, but see the investment order post linked previously for details. Often maxing an IRA comes before maxing the 401k.
The choice of Roth vs. traditional depends on your income. See
Traditional versus Roth - Bogleheads. If it's clear to you after reading that, go forth and do what is clear. If it's still a little murky, you might take your best guess and reply with "I think I should choose ______ now because _______." You'll likely get good feedback, with reasons.
Assuming investment gains, taxable is
never better than Roth. Whether traditional is better than Roth and taxable depends on your current marginal tax rate vs. the marginal tax rate when you would withdraw traditional funds. For most - but not all - traditional, particularly in the 22% and higher brackets, will be better than both Roth and taxable.