I would say Monk would be a decent start. Like I said, meta predictions are always a bit tricky, and it has the potential to shift mid season. Monk always has something going for it though, which makes it a great class every season, but only if you're willing and able to fill the required role. Support Monk has changed from a puller to a pull healer and back to a buff machine, so while it's easy to say you can always fill a support role, it's not always the easiest thing to do. I'd say your best bet is going either Monk, Barb, or Wizard, as they all have huge damage builds now and also have support roles that fit well into meta predictions, given that you don't have the Necro pack.
hey man, any idea if monk is a good pick for season 12? any prediction on whether it will be used in speed runs or will it fall back to rat runs again?
Meta predictions are always tricky, but the monk is pretty trusty as it brings a lot to the table in terms of group play. Also your Gift for the season is the Ulianna's set, so that's a pretty good start providing you find the right Cube items/weapons for the build itself (currently pushing into 88's without many ancients, and low paragons). That said, the support monk will most likely have a spot to fill when the meta gets settled. Something tells me people will be shocked, and amazed by the craziness that 2.6.1 brings to us. Current prediction on Speed Runs: 3 DPS, 1 Support.
Honestly, it depends on what you're looking for, if it's just a build for bounties or overall a strong single character.
The IK barb won't be a terrible start. Not only will you be working towards a meta build (possibly, but let's face it, Supp Barb will always have a place somewhere) but it can also weave in the Sage's set for faster early DB farming, and still has insane solo push. Overall, I think Barb has season 12 tied up, outside not being in the projected meta.
Trag Necro isn't terrible either and leads to a projected meta spot, coupled with the zNecro speed support build, makes it also a great selection to get started with.
DH, would be the build I would go for if it was just for bounties and nothing else. Without trying to sound like I'm bagging on it, UE DH would be the best torment/low GR farmer of S12, but without a meta, or support build, it won't see much in terms of higher GRs/Speed runs, projected, anyways