If you're super against sharing things with people, then your best pick is Oscar Peterson. Housings that include a kitchen will allow you to pick a cheaper meal plan and be able to cook for yourself on a budget, overall lowering your cost of living. The McGrath suites had one single room and one double room so it really depends what you're ok with, and had kitchen and all that good stuff so you don't have to rely on campus food unless you really wanted to (but from experience, and seeing the current offerings since covid, maybe not the best option). So the two floors were separated and you really only shared your space with two other people. I know you already stated a dislike for Erindale Hall though so perhaps I'll just focus on McGrath? From my understanding (though my info is a couple years outdated, take with grain of salt), McGrath housing was a two-floored townhouse, split between two groups of 3. It's not actually that bad, but when it matters, it feels like it really matters.
Of the two, Erindale Hall is much closer to everything and just makes your life easier if you wake up late on a test day (speaking from experience), whereas McGrath is technically double the commute. If cost of living is your main concern and you're willing to share a room with people, then your best bet is probably going to be either Erindale Hall or the McGrath townhouses (the double room variety). In terms of first year dorms, I really think it depends on the level of ease of access that you're ok with, the number of people you're comfortable living with, and most importantly (for most people, your mileage may vary), the cost of living.