Choosing a version of the Bible is hard, and to tell the truth I haven't done a great deal of research. I've read what various scholars have said about the versions, but I'm not linguistically qualified to judge the translations based on their own merits -- if I were, I wouldn't need a translation, I could just read the Bible in the original languages! The main reasons I chose the NIV are:
1. The NIV is based on more (quantity) and more recent manuscripts than just about any other version.
2. It was translated independently by several teams who then compared their results to ensure accuracy.
3. I find it very readable.
4. It appears to accurately translate the thoughts of the original texts into the appropriate English words. That is, it is a "thought-for-thought" (TFT) translation rather than "word-for-word" (WFW). The main problem I have with WFW translations is that the meanings of words change over time, as can be clearly seen by examining the way the Hebrew word sheol is treated.
Here's a chart of how sheol is translated in different versions of the Bible. This chart doesn't explain any of the other differences between the translations or why one should one over another, other than to mention that the person who compiled the chart is a Jehovah's Witness who believes that the New World Translation (NWT) is the most faithful to the original.
With a WFW translation it's very easy to think you understand the thought behind a word but be entirely mistaken. Some readers prefer WFW translations because they don't want to trust translators to attribute the right thoughts to the words... but they're still trusting the translators to put the right English words to the original words. It seems to me that even if you learn the original languages yourself you're still going to have to trust that your teachers are teaching you the language properly. Since you can't escape trusting someone, I prefer to cut out all the middle steps and just buy a TFT translation.