Which talent tree is it best to focus in? Or should I do an equal mix of two?

This is the hardest question to answer and its certainly up to the DK in the end as to what he/she wants to do,
but! as i have read over repeatedly there is no specific tanking tree they all do it,
but frost to me seems more tank like.

the problem lies in the fact the DK has no shield and mostly relies on DPS to hold aggro instead of using special aggro abilities (even though they have like 2)
I would say that Frost would be my first choice and Unholy my second for being able to pull group aggro.
Blood is very good at holding boss aggro because of its limited amount of ppl you can dmg. and you also slowly heal urself as your fighting making it easier for the healer.

i think these are how i would start but the unholy one i really cant depend on because ive never used it.

Blood - http://www.wowhead.com/?talent#jcEMqIhIcb0fosZbxx0hZ0x

Frost - http://www.wowhead.com/?talent#jcxZhxxxA0Ikf0fuzAo0x

Unholy - http://www.wowhead.com/?talent#j0xZhxxZbx0IpcbbouxzuIqo

To be honest, the best DK tanks i've met have been unholy. But that being said frost tanking is viable as well. Leveling unholy was a very easy experience as having aperm. ghould to taunt made soloing things fast and effecient. At the end of the day it really (blood) boils down to what you want to play!

Now get to work!

My buddy Dorkknight did a good bit of research on what is a good tanking build. I don't know if things have changed since I last played with him but this is what he told me. If you do the proper blood spec then you are a great main tank and boss holder, you have lots of self healing so it helps keep you going. If you do the proper frost spec then you are an excellent off tank since you have more aoe abillities so you can pick up aggro on adds quicker and easier. If you want a good build for tanking, just look up Dorkknight on Armory, he usually is in tank mode so you should get a good spec off of him. I know he checks out the Elitist Jerks website to get info on tanking.

id love to get lamastas up and tanking hes blood as of now lvl 72 just wisp vaviji if u wanna do some quests or what not, he needs to be 80