While leveling you should always que as a Tank, regardless of ur spec, just go Frost Presence, spread diseases and DnD. You will both top dps and tank like a boss
When you hit lvl 80 and u want to DPS, you DONT want to be Blood speced.
Blood is, out of all 3 DK specs, best suited for tanking, not so good for DPSing.
I would recommend going Unholy for leveling and after u hit 80 if u want to dps only, get dual spec and spec into both UH and Frost and chose the spec ur raid need the most.
The only diference in gear is 2H (UH) vs DW (Frost) weapons.
If you want to both dps and tank, spec into Blood as tank and chose 1 spec for DPS (UH or Frost ofc).
Whoever tells u Blood is viable as a DPS spec when it comes to low gear or any gear is a monkey.
P.S. stop linking stupid videos.