Also - you are correct that a backdoor Roth contribution is a conversion, so you've got to wait 5 years on that.
For me, the calculus is this:
If eligible for deduction and at a high-enough (this varies by individual situation) marginal tax rate - Go with Traditional IRA, up to the deductible amount if in the phaseout range.
If eligible for regular Roth IRA Contribution, do that.
Otherwise, if you don't have existing tIRA money or you can move any tIRA to a 401K or similar first, then backdoor Roth IRA
If you can't do a backdoor Roth effectively, then taxable account, along with any money beyond tax-advantaged accounts you're going to invest.