(Note: I'm a theological conservative / Evangelical / Reformed / Protestant. Take what I say with a block of salt.)
I think it depends on the amount of time you have and the type of study that you are doing. It should go without saying but it's always best to make this point explicitly: your first recourse is reading the text and prayer. Those are "free" and really the best investment of your time.
With that said, though I have access to the Greek and the Hebrew when I am preparing quickly for a Bible Study I often open up my favorite study Bibles (ESV Study Bible and Reformation Study Bible) to get a brief overview after reading the text or answer any surface level questions. I feel like the Bible Speaks Today and the Tyndale series are both very good at answering the types of questions that I have or pointing out things that I've missed and the series is very even (i.e. from what I can see all of the books are of the same quality).
When preparing to preach I have much more time and can go more in-depth: for textual issues in the NT I will look at Metzger, Comfort, and the NETS notes. For other textual issues I will consult more technical commentaries (though I don't (yet) own those in Accordance). Some of the public domain or historical commentaries are useful here - like Calvin or Matthew Henry - but only if I have time to sit and digest what they say. Finally, a commentary set like Pillar or NAC tend to deal with many of the issues that I wrestle with while thinking about how to clearly preach a text.
My best advice - pray and read, pray and read. My next best advice - think about the amount of time and the depth you need to go. Though I could crack open my Hermenia commentary there may be too much information! A study Bible may quickly and concisely answer my question. My problem is most often having too much information - getting on rabbit trails or too technical - rather than not having enough.