I disagree about Vega being third hardest.
True, blanka cannot use low mp, low fp, and low rh. None are safe really, at pretty much any distance (there might be a small possible window…but who are we kidding?)
Also true, blanka cant jump against top tier vega (air throw, vega jump rh/fp).
Nor is sliding really safe at any distance.
Yet, I still dont mind this match one bit, I even find it quite enjoyable. Why? As much as blanka’s normal stuff dont work to well, neither can Vega really do too much to blanka either. Basically, both characters kinda dance around the screen, never really attacking each other…vega staying in low mp range…blanka looking for that one knockdown to start offense.
So, I start looking at this match from a position of neutrality, neither opponent can do much to the other. Then I start asking…what should i do?
Luckily…blanka does have the fastest poke. Standing jab!! (im a broken record here). Though I admit I dont use it too much, focus attack has its uses in this match.
Basically, I see this match as being all about pushing the opponent towards the corner without attacking…just purely by movement. Once in the corner…let the elec spam begin. If blanka somehow gets a knockdown (i admit, i’ll throw out that rh once in awhile, or max max max range slide, which can be safe), more elec spam.
Yes, elec can sometimes whiff in wierd ways, but Ive found as long as its fp elec, it works well enough most of the time.
More overall picture stuff: Vega has to play really on target. If he lets blanka jump in and get close, blanka’s offense can be a nightmare, and vega dont have much of a reversal to stop it.
I only press three buttons in this match, jab, lk, and mk (rarely). (ok, and other buttons to make the elec come out, or for other special moves).
Thats just my gutt. I play a lot of vega. My vega has destroyed a lot of blankas. My vega cant play my blanka 
My blanka has also destroyed a lot of vegas (and they are all pretty solid too).
Ultimately, I dont consider vega to be that scary compared to some others simply because he doesnt have a scary offense. The kara throw/ downforward rh throw game that was soooo good in Super is a shadow of its former self now. Kara throw is good, but blanka standing jab keeps him out just far enough. Low mp is good, but it doesnt do tick dmg.
And see, thats the rub, thats kinda what this match comes down to for me. Tick dmg. Blanka has more opportunities to do it, and when blanka makes vega block, vega is pretty scared, whereas when blanka has to block vega, he aint that scared.
Top Three most difficult blanka matches off the top of my head and with no deep thought at all: Honda, Fei(i would love to play against aserious crazy fei), and Ken (I hope its my inexperience in the matchup, but ive looked for videos, japanese, anybody, and I cant really find any where blanka wins).