I started with Ketea as it seemed the best route (Ovni was not an option at this time). First fight no !! so just one card 2nd time I tried without a Whm and we wiped, disheartened I left it for a few months.
I went a 3rd time this week with LS peeps and got 3 with !! I then got the rest off Ovni which is indeed now quite often camped annoyingly by soloers most of whom wouldn't even let me get !! for them as Blm, without !! don't even bother with Ovni it's not reliable at all and your wasting yours and others time, striking a compromise with soloers is best as most people are after the card alternate with them some is better than none at all.
The biggest kick in the teeth was I got 6/6 on Ovni then while passing Shaolin belt the treasure pool shifted and in my haste I passed my card, instantly dropped party to get back in but was too late and no one got it ><.
If like me you have no reliable group of ingame friends you can just call upon at any time for Ketea then go with Ovni as long as you can consistantly land !! on it and get claim then this is relatively easy and you should see a card every other kill maybe more.
If you can muster up a decent full proc Blu Nin Whm Blm party with someone /brd at the drop of a hat and don't mind spending possibly 1.5 - 2+ hours getting a full 1 shot only tier 3 pop then Ketea is for you.
I'd personally aim to do both if you can though I certainly found Ovni to be less of a challenge to prepare for in terms of manpower and time.
Sounds like you had alot of bad luck which ofcourse happens from time to time. Ketea or Ovni or Carabosse are all viable routes. The fact that Ovni and Cara drop the card has taken strain of the T2 VNM in vunk. Remember changing the colour to a T3 pop has a good drop rate so you won't need to fight the T2 many times.
Best setup is NINorMNK, BLM/BRD, WHM, BLU. Its not even worth trying Ketea without stagger as you can't reset him.