Yup there are indeed those of us who do both, believe or not…heh.
To begin with, I’ve referenced DT’s over a number of years for mainly 3D modelling spec’d instruction, whether video and/or text/screencap format, to wit apart from, although not always the case generally, less favourable quality found via youtube, so yeah in my opinion, its fair to say Digital Tutors for the most part tends too resolve a sticky push-button workflow issue, primarily I find specifically helpful at times when applicable, rather than discipline oriented in depth technique/s per se commonly sought by most artists, so in effect user friendly tutorial library easily accessed, at an competitive price point, especially for those starting out or intermediate level.
On the other hand the Gnomon Workshop overall is aimed towards experienced/advanced users, hence not as specific in terms of guiding the viewer through instructor prompted que/teaching “hand-holding”, coupled on the whole typically assumes some familiarity with the app feature set functionality, therefore less tutorial runtime and on average [last I checked] more expensive to purchase, but TBH well worth the extra coin dropped, so easily in this instance - You Get What You Pay For.
Of course its entirely your call at the end of day which avenue proves a better fit, however that said, essentially since you’re prepping prior to course start, for the sake of “acquiring the basics” and/or “head start” in other words in regard to your CG area interest I’d recommend DT’s for the time being, remembering you could always reference Gnomon at a later date when time and circumstance permits.
Cheers 
