Whichever you A. have more of, or B. think are cooler.
The difference in dps at end game is small compared to how much dps a well built wf'd kensai is putting out. The difference for a 28 pt build, for a guy and his girl to experience the game together is next to nothing. Dont get all caught up in the dps is king stuff here and put something together to have fun.
Virtually any build can lvl to cap no matter how messed up. The question is how much frustration will the player experience on his way there. With your girl following you around able to heal you if you get in trouble, and you following her able to intim, and slice and dice if she gets into trouble, you guys will have lots of fun. Dont skimp on str or con, make sure you get the right buffs, and go wreak havoc on Stormreach
AC while certainly rewarding is more niche as currently implemented in game. There are lots of top notch players that tear up DDO's end game that have never, ever played an ac to to gear (not to cap but to fully geared). It can be fun, but it isnt necessary. Hitpoints and dr can be your defense, pull out a shield and block when necessary, body pull small groups, use landscape to your advantage, etc etc etc. There are lots of ways to defend in this game.
Ill give you a quick example of dps differences.
Back when the cap was 16, and we were dealing with lots of dps lag, had no pre's to speak of (no kensai or frenzied, we had tempest 1) a lot less stellar gear, monks still sucked back then, and fighters/barbs were low on the dps totem pole. We did a 13 minute normal shroud run. I think another server did it in 12.
Now the current record is 10 minutes, thats before the ToD nerf for monks in a monk heavy party. We didnt have ToD at the time.
So you say ok well the pre's and better gear, maybe the lack of lag made it a bit faster.
Our run was composed of mostly dex based ac rangers.
What at the time was high dps would be considered moderate to low now (granted tempest is different, but we also had less fe damage). The total time difference between a monk (ToD) heavy party and a dex ranger party was 3 minutes.
Thats a raid that takes on average 15-45 minutes depending on the group, at the time though nobody was doing 15 minute shrouds regularly. 20-25 were common among the speed runners.
The point is that the dps difference between 2 weapons isnt the end of the world. Yeah if you go to a +1 falchion to an epic sword of shadows you are going to notice a huge difference, but between the same great axe and falchion you arent going to see a difference in quest ease or completion. The question is do you like to see the biggest numbers seldom, or not so big numbers more often. Does 1 fit better in your concept of the build (if there is one) does one look cooler, do you have a stockpile of one over the other and not a ton of plat to retool etc.