XMR (Monero) is currently the leading CryptoNote coin. Some of the primary advantages are privacy enforced by ring signatures.  This addresses issues such as blockchain analysis, tainted coins etc. Unlike XBT where blockchain analysis can be a real issue. The other big advantage in my books is adaptive limits (which particularly means no 1 MB blocksize limit). Monero also has a very strong and growing community, it is rare among alt-coins in that is has a very fair launch. This is important when many alt-coins are plagued by allegations of premine, instamine, ninjamine etc. It has a good chance of making it into the top five and even the top three in my opinion.

What I suggest for anyone interested in XMR is to spend time doing the research, understand the community, what coins are direct competitors etc. I would start with the threads on this forum, the CryptoNote site  etc.

Here are some links to get started
https://cryptonote.org/ CryptoNote site
http://www.monero.cc/ Monero site
https://bitcointalk.org/index.php?topic=583449.0 Monero Announcement.
https://bitcointalk.org/index.php?topic=624223.0 rpietila Altcoin Observer
https://bitcointalk.org/index.php?topic=702140.0;all [XMR] rpietila Monero Economics.
https://bitcointalk.org/index.php?topic=700400.0  -> Monero Community Hall of Fame <- (Donations Thread)
https://bitcointalk.org/index.php?topic=683365.0 Microsoft Windows wallet thread (As a GNU/Linux user, I have little use for this thread)
https://bitcointalk.org/index.php?topic=622708.0 Monero (XMR) Speculation thread
https://bitcointalk.org/index.php?topic=597878.0 Monero Economy
https://bitcointalk.org/index.php?topic=721045.0 [XMR] Monero Community FAQ
https://bitcointalk.org/index.php?topic=652305.0 Monero Support

Edit: I will be adding more links that are relevant for research on XMR:
2014-08-14 https://bitcointalk.org/index.php?topic=740112.0;all Blowing the lid off the CryptoNote/Bytecoin scam (with the exception of Monero)