My setup is Mac Pro 3Gig Quad,Camcorder- Canon XLH1, I am thinking of adding a capture card for HD/HDV content creation, which would be a better choice AJA KONA or Decklink HD? or any other more cost effective solution out there with FCP 5.1.2? Thanks in advance

I would highly recommend the Kona 3. It can upconvert SD to HD, downconvert HD to SD (as can the Decklink)...but it can also CROSS convert 720p to 1080i and also do the reverse. Something the decklinks cannot do.

Plus AJA support is second to none.