The "best" selection will depend a lot on your party comp and on what you want from the item. You're also maxed on attunement slots (barring GM houserules) so you shouldn't just compare the benefits of each item, but also what you're losing in terms of a dropped item, for the items that require attunement. You're either losing 2d6 fire damage per attack from the scimitar, a summon from the staff, or AC/saves from the cloak.

Illusionist's Bracers would probably be your biggest damage upgrade, potentially doubling your round-to-round DPR since you don't seem to otherwise have Extra Attack.

The benefits of the Tome of Clear Thought are probably mostly outweighed by the Amulet of the Devout for your Wizard spells. +3 to spell attacks and saves is real juicy, and the bonus Channel Divinity is icing on the cake.

The Peregrine Mask is probably better than the Carpet of Flying unless you really need the transport capability for some reason, and even then I would probably recommend turning to a Bag of Holding/Tenser's Floating Disk. At-will flight is really good for moving around the battlefield, especially when you can blast away as a wizard.

Everything Daern's Instant Fortress can do (AoE, barriers) is replicable with the Staff of Power. You can do some fun stuff with a Ring of Spell-Storing, but mostly I think you'd get more mileage out of the Staff there too. This is your option if you want lots and lots of utility, and the other passive bonuses are great too. IMO, the Staff is your best OVERALL option, but as mentioned previously, it really depends on what you want to get out of this magic item.