I own both of these and I am about to go from responsive to unresponsive on my DMII.
I got the SPEC bearing from YYF’s ONE, and the SPEED bearing from YYJ’s Dark Magic II.
Is there a difference or is it just personal preference?
No difference whatsoever. Just a different brand of bearing
YoYoJam SPEED bearing is more SHINY.
Both work quite well.
There are some differences in construction but they don’t affect play in any way.
The Spec has 8 balls in it, and the Speed Bearing I have has 10 balls. I get a bit more spin out of the Speed bearing.
I have 2 Speed bearings with 8 balls and YYJ engravings.
And third one for some reason has 10 balls but does not have engraving.
YYJ bearings don’t have 10 balls in them, your thinking of a onedrop 10ball.
personally, i think the 10 ball is the best, it is much smoother, but i intend to get an terrapin bearing which is suppose to never need maintenance.
as for play, i find that YYJ and YYF bearing play very much alike, however YYJ bearings need to be broken in. while YYF bearings and unresponsive from the start, they tend to need lubrication much earlier than other bearings
- I received YYJ SFX from YYE couple of weeks ago and it has 10 ball bearing.
I thought it may be some sort of mistake but it looks like I am not the only one.
And later I received DM II and it has 8-ball bearing.
Sooooo it’s a MYSTERY
2)New YYJ SPEED bearings are pre-cleaned and play unresponsive out of the box.
NO, the sfx comes with a 10 ball. It’s probably a new trend for yyj.
Just because it has ten balls doesn’t mean it’s a one drop 10ball. One drop ten ball bearings have ten balls in them. That doesn’t mean others can’t.(There needs to be an eighteen ball bearing. Just for fun.)
didn’t you see patrick’s 22 ball bearing? 
Nothing is better than another. The standard YYJ Speed Bearing has 8 balls. The YYF Spec also has 8 balls. They’re are so similar to each other that there is literally no difference whatsoever.
wrong the yyj bearing doesnt have the same cage as a spec
And is that a positive or negative to the YYJ and YYF? If you think this is an important difference, which would you recommend. Give your advice.
personally, spec gives me more issues.
speed bearing.
when they are both maintained right, they both feel similar, but the speed bearing just feels a lot smoother, faster, and longer than the spec over time.
Alright, thank you all for the responses.