Rather play black or white?

> You don't think gambits are more dangerous in blitz?
Gambits are sacrificing material for some positional advantages. Usually for piece activity. Piece activity is very dangerous in blitz. But here the compensation for white is space advantage, which usually takes time to convert as you need to find good routes for you pieces. (Well, okay, the fact rooks are looking at the castling position is dangerous but no more.) Black will make some cautious moves like c6, d6 or e6, fianchettoes a bishop and will try to make white pawns move and be exchanged, keeping the black king on e8 as long as possible.

For example, in the Alekhine Defense, four pawns attack, white has a huge space advantage, engine gives a solid edge for white, but in blitz it tends to lead nowhere and even backfire as the pawns in the center become weaknesses. Just look at lichess statistics of this variation, black wins more often in most lines, even if restrict to high ratings. In contrast, in master games white wins considerable more often.

In the Four Pawns Attack I would argue that in blitz games between random players, the vast probability is that black is more prepared than white. Furthermore that specific variation is what most players who play the Alekhine want to see, because otherwise they wouldn't be playing it.