They are both top notch DAWs.
I prefer the look and feel and UI of Sonar, but Studio 1 has much better pitch and time stretching.
They both have great comping features and ARA integration is identical.
My crashes in Sonar are rare, but I've yet to have a single crash in Studio1
ProChannel and Fat Channel (Studio 1's version) are both nice to work with and great sounding.
I rely heavily on a large collecion of Waves plugins regardless of which DAW I'm using.
My primary interest in Studio 1 is the tight integration with the Presonus Series III Mixer/Interfaces.
It's a workflow I've waited years for.
Minus that software/hardware integration, I would only use Studio 1 for quantizing and editing the timing of audio. The UI is terrible looking and confusing. The track layers and sub groups don;t indent and all the shades of grey are the same.
Using other DAWs has definitley made me appreciate Sonar more. I hope Sonar lives on and gets even better under its new ownership.