Very hard to do as they all have different proficiencies and deficiencies that you can't equate directly to one another due to their varying attributes such as age, match experience and the tactical roles they are asked to play.
For instance if we signed Kiyotake we would have a greater threat from set pieces and a player with great vision to set up other people but your two other midfielders would have a greater burden to bare defensively as he is generally weak in this regard. You could sign Hughes who has shown glimpses of becoming a complete midfielder, very capable of all - master of none, and he would contribute more defensively than Kiyote but is not at the same level of picking out a pass as the Japanese national just yet.
The point to be made about any of those players you mention is that they would all, in their own unique way, add something to the squad that we simply do not have right now.
I'm less concerned about who we sign for this attack minded central midfield role. It's clear the team at Villa Park know it is an issue in the squad of 23 that needs addressing judging by the enquiries we have made. We don't know if Gardner can remain injury free and how he'll perform coming back and playing in the first team regularly. I'm almost sure we are going to sign someone, at somepoint this window, to start in this role.
You could consider it a knock on our current squad that we could bring in almost anyone for this position and it would be an upgrade. I'm looking at it more positively than that though. Whoever we eventually sign is going to make the side better. I think deep down every Villa fan knows this and that's why there is so much excitement, anticipation, and a fair deal of drama, about this position in particular.