For a beginner ? None. For Pros? The same. It's hard to be profitable.
45 ppl: only 7 places paid. It's hard to stay in the tourny - when bubble. 2 tables with 5-6 players. So you almost always should go all in (when you play) or your stack will be finished very fast, whatever stack you had.
90 ppl: when bubble - it's comfy table with 7 or more players. But tourney is longer, you need more skills to win more
hands.
Summary: for me 90 ppl looked better and more comfy while 45 ppl it's all about to stay in the tourny. Though I almost never won in 90 ppl tourney.
Just observe the tourneys before playing.