Barb/Monk should be at the top, WD will be very strong as well with the new Helltooth set. Think Crusader is the worst off this season.
I think on PTR WD was still last, though it's hardly relevant I think since it's only a few GR levels and you're not competing against other classes, unless you do group stuff, which WD are great at(cannon fodder pets to reduce chances of people getting one shotted and massive amount of +dmg debuffs and buff). New Crusader set is apparently pretty solid, and Roland is still good too, even though I dislike both styles.
Every class is viable really, has been forever. In terms of what class does the best without the best gear, it's hard to say.
Barb is nice due to having several whirlwind builds so you can build up a bunch of sets in parallel and climb the torment tiers quickly like this and there's a few alternatives if you don't like whirlwind, though they require good gear for it.
Monk is also nice due to having several exploding palm builds so you can do the same and there's a generator build if you just want to punch shit in the face but again requires very optimized stuff so you'll most likely farm as exploding at first(new set is explodin+SSS and is pretty cool).
WD has a bunch of viable builds but it's still highly dependant on specific legendaries on top of the sets(masks especially) so you'll need to use the cube a lot, so you'll have to run bounties. Luckily they added a new WD set that makes running bounties super super fast, like whirlwind fast, but you do need weapon+offhand from a 2set so annoying to get(it's hex chicken based though, you run around at like 200% speed with all the bonus and one shot packs easily in T7 which is what you farm bounties on for the most part).
Wizard has a lot of freedom on builds due to Tal Rasha and Delsere being fairly generalistic build(can work with random elements and with a large amount of skills and good 2pc bonus so strong right away). New set(archon) is kind of meh though unless they stealth buffed the belt back from PTR.
DH didn't get anything new but Natalya and UA are still good. I think you might be more reliant on getting several set pieces of a specific set before you can do good stuff though, but DH is also one of the quickest base class to do bounties with so shouldn't be too much of a problem.
Crusader got a new set, it's apparently good, but there's like 0 overlap with the previously good set, so you'll also need to focus on one specific set and complete the set asap, which means bounties again. Crusader is so so at bounties because horse is kinda shit until you're geared like crazy. Sounds pretty tedious to gear tbh.
