It's got to be Allegri coming in. It makes the most sense. I can't see them just writing this season off to go for Arteta in the summer
There are a couple of issues with going with Allegri, for me:
1) He speaks no English. Like at all. Even Emery spoke some English, and his lack of English has been criticised by some as being a reason why he didn't get the team playing together
2) He has said, back in 2012, that he will retire in 2022 at the age off 55 due to the stress, and before then he would quite like to manage the Italian national team (although with Mancini in role until 2022 this might not be possible). So it will be a short term deal.
3) He can be an overly defensive coach - Arsenal's strength is their attack, and I could see him trying to drop at least one of their forward line for another DM (which I don't think would work as well as just being more creative at the right time).
Poch is a significantly better manager, especially with the circumstances at the club.