One of the worst cases I constantly come across is people who cannot differencate bewtween "it's" and "its". The other ones would probably be missing accent letters (Pokemon instead of Pokémon), and the rest are just general misspellings.
As for that question, "lot of", "a lot", and "alot" are highly acceptable in the English-speaking world. & "lotta" is a bit acceptable in, let's say, talkin' street and catchphrases & whatever kids are doin' these days. I'm not grammer expert. It is what it is as people would say.