I think my old computer is on it's last leg and I have to get a new one. Can anyone give me insight as the best operating system to get (Windows 7 or Windows 8)?  I mostly use the computer for some recording in Sonar 8.5 and music notation in Finale 2012. Thanks for any help you can give me.

Well Windows 7 64 bit and 8.5 64 bit is a big improvement over XP for me. So definatly rule out staying with XP. I Have no experience with WIndows 8, I'm sure it is a great OS, next computer I buy will be W8 I would imagine. But, I think what's more important is your audio interface must have the drivers for what ever OS you choose, Software is not as fussy. 

I run normal XP Pro with Sonar 8.5 Pro but I agree with Cactus that it's probably best to go with Windows 7 now due to the fact that come April 2014, XP reaches end of life which means they'll no longer be any hotfixes for it.  I'll be upgrading my rig shortly to Win 7 Pro 64-bit!  I'd give Vista a miss too unless you already have it as Microsoft made hundreds of optimisations with Win7 so it runs much better than Vista.
 
Also, due to the memory limitations of XP 32-bit, it's probably better to go with Win7 64-bit as you'll be able to exceed the 4GB memory limit.  At that point, I'd also opt for installing Sonar 64-bit too!
 
However, before you get stuck into any major projects, just make sure all your plugins work, especially if some of them don't have 64-bit versions as some VSTs which are 32-bit only don't like running on a 64-bit host even with bit-bridging software!

I have Sonar 8.5.3 running on o triple boot computer: w7 32, w7 64, w8 64. It works fine on all. 
 
For windows 8 The main problem was finding a driver for the sound card. I am using a beta for a slightly different card. Mostly stable now. Except when I open/close lots of projects. Working on one project for hours seldom results in sadness.
 
The crashes nuke sonar, but do not freeze the machine as the older driver did.
All crashes are caused by the sound interface driver. Not sonar.
 
I have the auto-save enabled. And I ALWAYS save to a NEW name every 10 minutes or so.
 
Example: "Great Project 1013 a.cwp"   and then "Great Project 1013 b.cwp" This way I lose very few edits/changes.

Thanks for all your feed back, I appreciate the help.    
 
John