I'm a little confused...are you looking for a putter that will help with longer putts or a mid-range that will will be a good approach disc?
As far as putters go, I use 3. I have a DX Aviar because if I need a putter to sort of turn over or just wrap around an obstacle that's my go-to disc. I also use this an approach disc at times. I also have a Champion Aviar that refuses to turn over and will hold a straight line, this is what I use for any straight line putt and will give me the best chance for longer putts. I'm also working in a SSS Wizard into the mix because sometimes my Aviars are just too stiff that day and the wizard will grab chains all the time! :)
I bought a Nuke, but I personally can't throw the thing. I've had a little better luck with the Katana but not much. I don't have a cannon for an arm though, so if you do you'd probably have better luck than me.
I like to use my Discraft Stratus for long putts. Get a nice light weight version of it (pro D is my favorite for putting, but that's me) and go to town. It has significant glide and predictable fight paths.
I prefer an Innova XD for mid-range and long putts. It has a nice low profile and fits well in the hand plus it's dx plastic so it's inexpensive. I would probably go for max weight for windy days. It hold a straight line pretty well.
I say a Roc and a Buzzz. Two must have discs. As for helping on longer putts. I use a Classic Roc for those 100' to 125ish up shots/putts. Innova says it's a putt and approach disc, but I never thought of it as a putter. It's a great disc imo.
The classic Roc in anything but Star plastic is great, otherwise it is a stable pig. Which is good for upshots or headwinds. Some people like ridiculously stable putters, if that is the case then the Star Classic Roc is for you.