Currently? It's hard when I personally don't rate a lot of our players highly

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I'm hoping Emery can change my perception of these players or that they're not as mediocre as I think. But from what I have seen, I just don't feel like we have the right balance/calibre of players at the moment.
Anyway, assuming all are fit on their day, I would go with:
Cech, Bellerin, Koscielny, Holding, Monreal; Elneny, Ramsey; Aubameyang, Ozil, Mkhitaryan; Lacazette (4-2-3-1).
That being said, Cech needs to be upgraded. He's a decent goalkeeper, but age is quite clearly catching up with him.
Koscielny has been a great servant for us. His Achilles problem is affecting him massively and again, he's no spring chicken. Need to upgrade.
Holding or Chambers over Mustafi when both are available for me. The latter is just too rash and indecisive. Wouldn't bat an eyelid if he's sold this Summer.
Monreal was probably one of our best defenders last season, somewhat surprisingly. He's always been a solid left-back, but he added goals to his game which, at the age of 32, was unexpected. I think left-back is a position we do need to look at though, as we have no long-term player for that position. I'm not 100% sold on Kolasinac; had a promising start for us, then got injured and never recovered afterwards.
Elneny as our deep-lying defensive midfielder because he can press well, is a decent tackler and has a good work-rate. Keeps possession ticking over nicely too. Again, though, good squad player to have, but not the required quality for the first-team. To be fair to Xhaka, he did ok towards the end of the season, but as I've mentioned before, generally he is too slow to release the ball, gets caught dawdling in possession and isn't dynamic enough to be an effective DM. So this is a position that needs to be strengthened urgently.
The rest are self-explanatory I'd have thought.
It might be surprising I've included both Aubameyang and Lacazette in there, but they actually formed a good partnership together when in the same side. You may think it's bizarre to boot Aubameyang out wide when he has an impressive goalscoring record for us, but he does have a habit of drifting inside and sometimes switching positions with Lacazette during the game.
Right now, that team needs several new additions to compete for the top 4 spot though. We simply cannot go into the season with a starting XI like that.