I'm using Sonar, but I've been on it for years. The high end version of Sonar comes with Dimension pro and Rapture, which are both pretty cool V.I.'s, as well as Melodyne, VocalSync, and Addictive drums 2 + 3 addpacks. The processing plugins sound pretty good as well, but I use mostly UA and Waves stuff.
As for strings and symphonic stuff, I think you'll probably want to buy a third party V.I. no matter what DAW you choose. I'm running NI Komplete and it's really good and covers everything you could want.
The only thing I would point out about Sonar is that the midi editing and the Score are not as well developed as Logic and that could be an issue depending on how you compose your pieces.
My advice to anyone purchasing a DAW is to try them all and find the one with the most intuitive workflow FOR YOU. They all do the same thing, but the workflow is drastically different across platforms, and can be really frustrating to use if it's not intuitive to use FOR YOU. ( I find Logic the most byzantine, backward piece of software I've ever encountered, but that's just me - people love it, so there you go...
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I guarantee you'll end up buying third party instruments and plugs no matter what platform you purchase, so I always encourage people to focus on the workflow and not the freebies.
Hope that helps