As already suggested, the HSA (if your HSA allows good investment options) may be your best option - but check.
My HSA is definitely not an investment account currently. It's some sort of checking account or something at a local credit union...I get "Dividends" but we're talking like 0.5% APY. I'll have to look into whether it's possible to move it to some sort of investment account...
Usually it's an option inside that checking account. Some companies require 1,3, or 5000 in cash to stay in that account while the rest can be invested. The power of HSA first is that instead of being JUST pre income tax, it's pre- social security and medicare (~7% of w2 income) and pre-income tax.
So instead of making $75,000 before any taxes you're making (with family plan) $68,250.
That means your FICA taxes @68k are $4777.5 instead of $5,250.
Now for income tax you then start at 68k instead of 75k and then subtract your 401k, but only your contributions NOT the match. If you can please edit your OP to show how much the employer match is.
If your wife is non-working you can pay into an IRA for her as well.
Since you are asking solely about Tax focused retirement accounts your eligibility for 2017 should look something like this:
HSA: $6,750 max
401k: $18,000
His tIRA: $5,500 fully deductible at that income level
Her tIRA: $5,500 fully deductible at that income level
Totally: $35,750
So taxable income would be roughly $40,000 now spending aside maxing all those vehicles would probably get you close to a 0 dollar income tax bill, that with 2 children and refundable credits would still give you a refund.
That being said I'm no MDM, or CPA. If you're IRAs are at Vanguard regardless of the options inside your 401k it's probably in your best interest to do your company match then both IRAs after the HSA.