The short answer to this question is: the one you’ll read!
The longer answer takes some factors into account. For just reading the Bible, any translation that you can understand is sufficient. But for studying the Bible, you want to avoid translations that are too heavily paraphrased (like “The Message” and “The Good News Bible”) because too much of the character of the original text is lost in updating the vocabulary.
For serious study, word-for-word translations are the best, although they can be clumsily worded because they can tend to force qualities of the original language (like word order) into the target language.
For our study, I recommend a translation that emphasizes fidelity to the original language without sacrificing readability in the target language. One fine example is the “Revised Standard Version” (and I recommend specifically the Second Catholic Edition, such as is published by Ignatius Press). This translation uses “formal equivalence” rather than “dynamic equivalence”, which means it is closer to word-for-word than thought-for-thought, but it is still readable and understandable. This translation will be abbreviated as the RSV.
Another translation I recommend is the “New American Bible” (revised edition), which you can buy at bookstores and online, and which the US Catholic bishops have made available free online. This is the translation that our Lectionary is based on — that is, the readings we hear at Mass are based on this translation. This translation will be abbreviated as the NAB.
An additional factor to consider in choosing a translation is whether the vocabulary is modern or archaic. Compare these three translations Proverbs 4:11-12:
|4:11||I have taught you the way of wisdom; I have led you in the paths of uprightness.||4:11||On the way of wisdom I direct you, I lead you on straightforward paths.||4:11||I have taught thee in the way of wisdom; I have led thee in right paths.|
|4:12||When you walk, your step will not be hampered; and if you run, you will not stumble.||4:12||When you walk, your step will not be impeded, and should you run, you will not stumble.||4:12||When thou goest, thy steps shall not be straitened; and when thou runnest, thou shalt not stumble.|
If you only looked at the King James Version, you might assume the word “straitened” (in verse 12) is an older spelling of “straightened”, but puzzled as to how that word makes sense in context: “when you go, your steps won’t be straightened”? God will let you walk crooked lines?
The other two translations use more modern language (“hampered” and “impeded”) that should clear the issue up: “straitened” is not the same word as “straightened”. Consider the geographical feature the Strait of Gibraltar. A “strait” is a narrow passageway in the water, which is sometimes not navigable because it is too shallow or has reefs or rocks that prevent safe passage. To have your steps “straitened” means to have your steps blocked, to have your way made difficult by obstacles.
What Type of Bible?
The simplest form of Bible is one that simply has the text of the Bible, and nothing else. That is fine for reading, but not very helpful for studying. It should also have a table of contents!
When engaging in Bible study, you want an edition that at least has cross-references that give you connections between verses of Scripture. For example, when reading the passage in Matthew 8:1-4 about Jesus healing a leper, it is helpful to see that this passage is connected to Mark 1:40-44 and Luke 5:12-14.
Another helpful feature of a Bible when studying is footnotes that provide simple commentary on certain words, phrases, or passages of Scripture. For example, in the Ignatius Press RSV, there is a footnote on Matthew 10:5:
 These Twelve Jesus sent out, charging them, “Go nowhere among the Gentiles, and enter no town of the Samaritans,*  but go rather to the lost sheep of the house of Israel.”
* 10:5: The gospel, the Messianic salvation, had first to be preached and offered to the chosen people, Israel. Later it would be offered to the Gentiles.
This footnote provides a bit of context to the exclusionary-sounding command of Jesus to his apostles.
Next, it helps to have a Bible with introductions to each book of the Bible, explaining a bit about the book (what time period it covers, where it takes place, etc.). The NAB has an introduction to every book, whereas the RSV only has introductions to the Old Testament books.
A thorough study Bible will have commentary throughout each book of the Bible. This goes beyond simple footnotes; this commentary provides deeper description of people, places, and events, and can even include word studies (explaining vocabulary in detail). In a Catholic study Bible, the commentary will often make references to the Catechism of the Catholic Church and to other ancient authorities (known collectively as the “Church Fathers”).
Finally, some study Bibles include maps, concordances (an index that shows important words in context), and reflection questions.
I strongly recommend the Ignatius Press RSV Study Bible. Right now, only the New Testament is available in a single volume, but it is definitely worth it! The Old Testament books are becoming available bit by bit, eventually working toward a single-volume Old Testament study Bible. The Ignatius RSV Study Bible has plenty of cross-references and commentary, with maps and a concordance at the back.
If you can afford it, I would recommend having two Bibles, if only so that when studying God’s Word, you can read the text with two translations and two sets of notes. Multiple perspectives can be very helpful.
Owning a Bible means that you can write in it. Get a Bible you’re not afraid to mark up: get a pen! Circle things; underline things; write questions or comments in the margins. Add your own cross-references.
While you’re writing in your Bible, you might as well also get a highlighter to make sure certain things stand out visually.
If you are having trouble finding books in the Bible quickly, consider buying Bible tabs. These are sticky tabs that you apply to the edges of the first page of each book in the Bible, so that you can quickly turn to Matthew, or Romans, or 2 Kings, and so on. I strongly recommend the Bible tabs from Ascension Press’s “Great Adventure Bible Timeline” study materials. These tabs are color-coded to help you remember where in the timeline of the Bible a book takes place. You can see these tabs in the header images of this blog:
The Internet makes it less necessary to buy a Bible dictionary, as there are many available free online. But if you are going to buy one, I recommend the Catholic Bible Dictionary.
Finally, having a copy of the Catechism of the Catholic Church (or using my online Catechism search engine) is very helpful, if only for the Scripture index at the back. You can quickly find paragraphs in the Catechism that refer to a verse or passage from the Bible (e.g. Luke 10:27).