FYI ALL.
I didn't know about this particular trial until I found this thread a few days ago. I thought that I would be a good candidate to put your theories to the test, since (until I saw this thread) I have never used any character, aside from Milles Blanche something something. (Heh.. sorry. The actress chick. I'm quite a manly geek in RL, but in games, I like to cross-dress.

)
I reached level 50 about a week ago, and ran out of "drive" to play, so I started going through the list of trials.
Enough of that... without further adieu, my results:
These results were achieved on the XBOX 360 version of the game, so make of that what you will. My suspicion is that it is probably the same for each system.
#1. When I finally received the "Split Personality" award, I had
JUST PICKED MY LOADOUT AND WAS DROPPED INTO A MATCH WHICH WAS COMPLETING. Luckily, I was assigned to the winning team. The game type was CAPTURE THE SISTER. (Literally JUST dropped in. My feet didn't even hit the ground before the "YOU WIN" graphic popped up, follwed by the "Split Personality" info box.) I was using Naledi Atkins when this occurred.
Starting from the beginning, the middle, or the very end of a match appears to have no bearing on this trial.
#2. I'm a good player, but certainly not a great player, by any means. As such, I rarely come in at the top of the pile for any gametype. For these matches, I was ranked from the very top to the very bottom at random in random game types.
Individual rank during a match appears to have no bearing on this trial.
#3. I played all gametypes EXCEPT for Civil War, Last Splicer Standing, ADAM Grab, and Survival of the Fittest. (EG. Turfwar, Capture the Sister and Team ADAM Grab.)
Team VS individually ranked gametypes appear to have no bearing on this trial.
#4. My cable connection sux, so EVERY MATCH I PLAY is cursed with lag.
It would appear that LAG has no effect on this trial.
#5. As stated, I play on the XBOX360, so I do not have the ability to snap a screenshot, however, I do have a camera on my iPhone and I will happily snap a photo of my trial statistics to show that I have received the trial award. I will edit this post and add link to photo as soon as I run in and snap the pic.
For those of you who think that you've
"already won AT LEAST 5 matches with each character", I can only say this... you are probably mistaken. It took A WHOOLLLLE lot longer than I had first imagined to accomplish this trial. This was, in most part, due to all of the games lost. I honestly did not realize how many games are lost in any gaming session, because you can lose the game as a team, but still have a great game as a player. Perception is the key here. I usually have 2 or 3 games where I "feel" like I PWNED NOOBS TEH UBERRR! and then have a game or 2 where I'm just completely off. After recording my scores and team scores, it blew my mind to go back over them and realize how many of the games my team actually lost, even though my perception was that they were all good (read:WIN) games.
Granted, we all want to be on the winning team for every game, but you most likely are thinking of your time spent PLAYING and not the matches that your team actually WON. Also, If you're playing private matches, they don't count against your trials. (Which I thought was obvious, but just to make sure all bases are covered...)
For those curious, I've posted my recorded match data below for a few characters.. It's a crapload of info to type, so I only included a few to give you some idea of what my "experiment" looked like. If anyone wants the rest of it, let me know... it's just too damned much to type without provocation:
(This list is way out of order, in relation to the character selection screen, so, sorry 'bout that.)
WINs with *'s after them are matches that I joined already in progress.
Also, I know there are some characters with more than 5 wins... In most cases, this was due to finishing a game, then being sent to the lobby, then being immediately sent into another game without enough time in between to switch characters.
TW=Turfwar
CTS=Capture The Sister
TAG=Team ADAM GRAB
Character Gametype My rank Team Rank
-----------------------------------------------------------------
Danny Wilkins TW 3rd Lose
TW 4th
WIN
TW 1st Lose
TW 3rd Lose
TW 1st Lose
TW 5th
WIN*
TW 2nd Lose
TW 1st
WIN
CTS 3rd Lose
CTS 3rd Lose
CTS 1st Lose
CTS 4th
WIN
CTS 2nd Lose
CTS 4th Lose
CTS 1st
WIN
TAG 1st Lose
TAG 1st Lose
TAG 5th Lose
TAG 3rd
WIN*
TAG 2nd Lose
TAG 2nd
WIN
---------------------------------------------------------------------
Milles deGlace None None None
---------------------------------------------------------------------
Jacob Norris TW 3rd
WIN*
TW 1st Lose
TW 4th Lose
TW 6th Lose
TW 1st
WIN
CTS 4th Lose
CTS 3rd Lose
CTS 3rd Lose
CTS 3rd
WIN
CTS 1st Lose
CTS 2nd
WIN
TAG 2nd Lose
TAG 1st
WIN*
---------------------------------------------------------------------
Barbara Johnson TW 3rd
WIN*
TW 1st Lose
TW 2nd Lose
TW 4th
WIN*
CTS 3rd Lose
CTS 1st Lose
CTS 2nd Lose
CTS 1st Lose
CTS 1st
WIN*
CTS 2nd Lose
CTS 1st Lose
CTS 3rd Lose
CTS 1st
WIN
TAG 4th
WIN*
TAG 2nd Lose
TAG 4th Lose
TAG 1st Lose
TAG 5th
WIN
Buck Raleigh
Suresh Seti
Naledi Atkins
Zigo
Oscar
Louie
Hopefully this will help some of you get the trial. I'm glad I did... but I probably don't want to do it again.