I've had account at Infinity for the sole purpose of betting parlays. Their payouts are legit on point-spread parlays. Occassionally they have games at -115/-105, etc., but no more than any other standard -110 book.
I wouldn't play baseball parlays there b/c they cap the payoff but don't tell you until after you confirm the wager (or at least they did a couple years ago.... I don't use them for baseball now). There are things I really don't like about infinity like having to use a second password for withdrawls that can be forgotten when you don't use them for two years like I did between 2003 and this fall, and having to call for a withdraw instead of using the webpage, and having to pay $15 for every withdrawl (at least neteller).
But the parlays are definitely legit.