First, I acknowledge that study notes aren't infallible, and aren't the inspired work of the Holy Spirit. I know that they're written by humans. They can be good--great even. But they're not to be taken as the absolute, undeniable truth either. You may find things you disagree with in individual notes--you may be disagreeing because it's unbiblical, or you may be disagreeing because you simply don't like what is being said. There is an important difference! Study notes should always be read with an open-but-discerning mind. Tested against the Bible itself. Tested to see if the notes are logically connected with the text of the Bible itself. (Does the Bible say what they really said it meant?)
That being said, there are some GREAT study bibles out there. And they can offer so much to the reader--insights into the background, culture, society, history, language of the Bible (Old or New Testament times). They can provide maps, charts, illustrations, lists, dictionaries, concordances, cross references, etc. Some study bibles are light on notes, some moderate, some heavy. There are different levels of intensity offered to readers.
You *really* need to browse through any study bible before you buy it. What one person loves--finds useful, finds essential--might not be right you. There are still so many little elements to finding the right Bible: one column or two? cross references? red letter or black letter? (that is the words of Christ in red or just in black like the rest of the Bible), paragraph format? verse format? page thickness, layout of margins, size of font, the darkness/lightness of font, paperback, hardback, imitation leather, bonded leather, genuine leather, genuine calf leather, thumb-indexed, etc.* You won't know it--that this is the one--until you see it, you feel it.
My suggestion--go to your local Christian bookstore--or if that's not an option, your local bookstore (or local used bookstore) and browse to see what is available. Opening it up, browsing through sections--seeing what the book introductions, outlines, charts, maps, notes, etc. are like--is the only way to know if it's what you actually want. If you've got a favorite passage or two, you might want to open to that and read the notes that go with it. Get a feel for how the notes are presented, arranged, their depth, their content.
Be patient. Better to take your time and be satisfied than to buy too quickly and end up frustrated and unhappy and wishing you'd bought something else instead. I think you'll find each one has pros and cons. It's finding what works best for you. The ONLY question that matters--when it comes down to it--is this: Will you use it? Or will it just sit on the shelf? It doesn't matter what Bibles I think are best--or which ones have the most 4 and 5 star reviews on Amazon--it matters if it is you-friendly.
Here are a few of my favorites
MacArthur Study Bible -- available in New King James Version and New American Standard Bible. The volume of notes for each book/chapter is amazing--astounding even. Very detailed, very exhaustive. Written by John MacArthur. He is a Baptist. There are a few notes that emphasize immersion over sprinkling and believer's baptism over christening/infant baptism. But except for those, I think these notes are notes that almost all Christians (Protestants at least. I'm not a Catholic so I can't *guarantee* that the notes will suit Catholic believers. There could be some issues there, I can't say one way or another) can benefit from regardless of denomination. Definitely the study bible with the most depth and substance. But the length of the notes (even though they're high quality) might be intimidating to some.
Nelson Study Bible-- available in New King James. This one is now being marketed and sold as the NKJV Study Bible (Second Edition). With each edition/reprinting/redesign (since its initial one...the word Nelson's has become smaller and smaller until it's disappeared altogether) but it started out life as Nelson's Study Bible. I own THREE copies of this one. Four if you count the one I used to have but gave away. I first had it in paperback--gave it away when I bought it in leather; second I found a used leather copy for under $5 and couldn't resist; then I succombed again to the personal-size-leather edition. Which goes to show you that I'm either really crazy OR that this one is really good. What I love about this one? The notes are thorough--almost but not quite as many as MacArthur--but this one has the added bonus of highlighting and defining various greek (and I believe hebrew words too) words and giving just that much more substance to what is being presented.
ESV Study Bible -- available in ESV. This is one of the newest study bibles released. (And I think one of the most user-friendly I've seen.) I've just had mine around three or four days. So I haven't explored all its features yet--but it seems to be good. I like the fact that buying any of the editions of the ESV Study Bible will give you access to the online edition of the ESV Study Bible--including features available only online.
The NKJV Chronological Study Bible--while not as thorough (heavy) as the MacArthur or the Nelson--it offers a unique look at the Bible. It is presented in chronological order. Extra emphasis is given to placing the Bible within its context--history, society, culture, religion, law, language, literature, etc. It's definitely got something unique to offer readers that the others on this list do not.
There are other study bibles out there--NIV Study Bible (Zondervan) Life Application (so many options it's unbelievable), Quest, Open Bible, Ryrie, Spirit Filled, Scofield, etc. But I personally never found them to fit my needs and expectations. But if they work for you, then great. I won't criticize your choices! I'm not dismissing them as unworthy, they're just not for me.
*Do these details really matter? You might be surprised! People who will not buy a bible because it's one column and they like two columns (or vice versa); Or people who won't buy a bible because it's red letter and they only like black letter; Or people who won't buy a bible because the pages are too thin and you can see the text bleed through from the other side. So yes these crazy details come into play.