I've been using Pro version for couple of months. It was around 350€ so it's one of the least expensive DAWs and it's a pro version without any limitations. The great thing about Studio One is that it's easy to use. The user interface is well designed and doesn't require you to read help files to figure out stuff. It's really easy to start writing songs and try out different things.
The number of built-in instruments are limited, but maybe it's just good. You don't get lost in having too much options. There are four built-in tools: Mojito which is a monophonic synth, Impact (sample player with sample library), Sample One (basic sample player) and Presence which has some kind of internal sound type with a number of options to tweak the sound, including effects section.
There is also a good amount of effects to lay over sounds. You can also use Ampire XT as an effect. It's a virtual guitar amp with stomp box section, having the typical effects of a pedal board.
Then there is Native Instruments stuff you can download, including Reaktor, Kontakt and Guitar Rig. I haven't really tried out them that much, other than Guitar Rig. It had a huge latency and ridiculous amount of noise coming from some mystery place so it's not good for recording guitar.
Studio One (64bit version to be exact) doesn't have an internal engine to run 32bit VSTs like some other DAWs, but that's more the problem with VST developers, because there should be 64bit native versions to run in 64bit DAWs.