I recommend against MSSQL not because it's not a good DB (it is -- it was originaly Sybase) but because it's cumbersome to work with outside of the Microsoft ecosystem. You mainly interface with it using ODBC and that's a pain outside of Windows. You're stuck with windows boxes on the back end AND on the front end. You can add ODBC systems to the mid-layer/server boxes you'd rather have (Linux, usually) but now you're paying money to add a kludge. Furthermore, because it absolutely needs to run on Windows on the back end, you have to pay employees who are generally of the sort who are going to want more Microsoft tools, so you'll be creeping more and more away from free stuff which is easy to maintain to a bunch of licenses and a complex setup. (Had to get a bunch of Windows boxes set up with precisely this sort of issue just a few weeks ago -- man! was it painful.)
You could start your project with Postgres and find out why you're unhappy with it and plan for a migration to something which is better for you post-hoc: Don't write SQL procs, and don't weave your SQL through a whole lot of code. Though frankly, the suggestions for Red Shift seem right on the money. They use Postgres drivers, JDBC, and ODBC, so you're set on any platform you want to work on without any added cost. They have a two-month free trial. You could try that out first and figure out what you're unhappy with there as a first step. Same rules apply -- keep things simple.
DBs are not for chewing data -- they're for giving you just the data you need so you can chew on it. You use the right tool for the chewing job once you have the data. (Some DB pre-chew is fine in situations where it's efficient and easy -- group by's, mostly.) So it doesn't matter that much how long the feature set of your DB is. What matters is that it's fast and you can get data in and out of it just about anywhere you want to. I've seen shops where they do all their data chewing in SQL server. They write reams of ugly, ugly code. They do this because they know how, and don't realize that a little work learning other things would make them vastly more efficient. The thing to always remember is that you don't buy a hammer and assume everything is a nail. Buy something which works with lots of other tools and pick the right ones for your job.