Finishers, IMO, always have to be one of three things:
1) Unique or different in some way - When I was first making characters, I wanted finishing moves that were unique and took things a bit further. Some of them defied reality, most notably the corkscrew shooting star press that Black Zack Dragon did. The RTD was more realistic than that, but in 1999 it was mostly unheard of. Brock Lesnar made a less head-droppy version much later (2003?) in the F-5, and the motion of Christian's finisher mimic's that movement, except instead of a flat front bump the wrestler gets headdropped. Both maneuvers are similar in that both of them were extremely different moves for their time and it made them more noticeable.
2) Looks legitimate - Christian's MDK finisher looks like it
will fucking kill someone (fun begins at :15):
http://youtu.be/C2Na0o9Q90o. Finisher's should have that effect, regardless of whether you're big or small. I think that's why the superkick caught on when people were efedding smaller guys: it looked legitimate and there was documented history of Michaels winning massive amounts of matches against basically anyone regardless of size.
3) Different or executed better than 98% of the wrestling world - if there's one thing the "E" has proven, it's that certain moves are just deadly when "executed correctly" or executed by the right people. Sure, everyone in the "E" throws punches, but when Big Show punches you in the face, you get KTFO. Similarly, a lot of indy-type guys can do a moonsault, but Daniels does his BME different from everyone, and when he executes it, it's perfect-looking. See also: everyone does superkicks but Jeff Andrews and Cancer Jiles KO someone with them, while other guys get 2 counts.
You also have to know your audience and know what will get over as a finisher in the territory. An example of that is a little story I heard from a small fed elsewhere. A decent-sized local name with a bad attitude was booked in the main event of an indy fed show, and he got into an argument with two respected regular upper-midcarders. The issue of contention is that the local name had showed up and made a big deal about how he wasn't going to watch people that weren't on his level. Typical high-horse bullshit. Two of the UMC's took exception and got into an argument with him until it was separated backstage with little to no resolution.
So the UMC's decided to go out there and send a message to the LN.
The LN's normal finisher was a running Ace Crusher. The UMC's, during their match against each other, executed some high number of running Ace Crushers between them. I swear, it was like a transition move for the match, it was done like 10 times between them in a 15 minute match, all for 1.5-2.25 counts. So, later on in the night, when the "name" came out and did his one Ace Crusher and pinned the guy, the crowd was dead and he couldn't figure out why. He could still not know why for all I know, I'm not sure if anyone told him. But the point I'm making is that you have to know your audience. Had he seen that match, besides being outraged, he could have audibled the finish into something that would be more over with the crowd. Similarly, your finisher could be a badass-looking 360-Degree Sattelite Headscissor Burning Hammer of DOOM~!, but if your audience is desensitized to headdrops it won't be nearly as effective as, say, a badass-looking Sharpshooter.
My personal flavor depends on the character. If he has no set strategy or theme, a headdrop is a good way to put someone down for the three.
