I would like to throw HaloPro
out there to be added to the list.
Version 1.3 has been flawless in MSV.
It is extremely accurate and I have it tuned to incorporate the Halo bug (which other range addons do not do, so they can show you in proper range but still miss - HaloPro will never miss with a green light). I have manually spent hours and hours and gotten feedback from other priests that a green light does produce the best damage with Halo.
It's very customizable, and I add new features as the community requests them, and it is tailored specifically to Halo.
I also believe it is a very important tool to priests as without a range addon, you're always somewhat guessing at your range. If nothing else, by having, and practising, with an addon such as this you get a much better feel for proper range and are able to anticipate and move quickly to proper position for Halo as it comes off cd. Know the sweet spots in your strategy to stand for it etc. Again with an addon like this, you're relying on using other 30 yard range spells for indicators (and probably missing or doing less damage as a result due to the Halo bug), or not maxing Halo's potential.
I wanted to make sure HaloPro was up to snuff before posting a recommendation for it, and v1.3 is ready imo. :)