For starters, congratulations on reaching your savings comfort level. Don't forget to give yourself permission to tap into it if a real emergency comes along (this is something I struggle with).
For your savings now, I'm personally a big fan of maxing out the HSA. They have a triple-tax advantage (no tax on deposits, no tax on earnings, no tax on withdrawls) as long as they're used for a qualified medical expense. If you never use the money, you're allowed to draw down at your income tax rate at retirement level just like a traditional retirement account. The way I see it though, if you're young enough, you will have one or many medical expenses in your lifetime that will exhaust it, whether it’s a pregnancy (yours or partner’s), ER visit, cancer, heart medication, joint surgery, etc.
If you max that out, I personally like maxing the Roth accounts next because I like the flexibility they give in allowing me to withdraw penalty free if I really wanted to. This may or may not be the next best tax-advantaged account, but that strongly depends on your specific plans and lots of assumptions about what the laws will be in the future.
Bottom line, all of these are good choices, they just have different sets of pros and cons.
