Run Block Tech - 70+
Conditioning and Toughness 70+ high energy makes a big difference
Run Block Power - Depends on position and play type
Quickness and Speed - varies by position and opinions vary on speed
Power is the big question because it's very expensive. One philosophy is to go tech-blocker and get enough power to stay on their feet (35-40)
The other option is to get both and make sacrifices in other areas, i.e. pass blocking.
Power can be killer on inside runs, especially with Goal Line Blocker, but you have to give up a lot of other things to get it to 70
Quickness and Speed matters most on guards on the outside running plays, the ones where the guards pull and try to seal the corner
It can also help a center get out on the LB
Tackles probably don't need as much
Blocking is a series of interactions, i suspect quickness makes it easier to sustain/regain blocks
Opinions vary on Balance - I like getting 50-60 to keep the guy on his feet and sustain/regain blocks
Sacrificing Conditioning probably isn't a good idea
Because Blocking skills are so expensive, it's really hard to max skills, so the Early Bloomer trait is widely used - but this forces you to put more points into Stamina
A widely used Tech Blocker setup is Early Bloomer/Tech Blocker/Run Blocker
Tech Blockers don't need much Strength, which is what you usually exploit on the Early Bloomer setup
Don't forget, you get a career total of 3 Cap Boosters that can increase a skill cap by 5 points each
If you go for Power, you may want to substitute Meathead for Early Bloomer
You can play with builds using the free calculator
http://glb2-player-builder.herokuapp.com/or the GLB2 Scout Tool
http://www.glb2scout.com/