I known my sisters just flew, with Frontier, and IF you booked directly thru Frontier, then you didn't get an additional $25 charge for carry-ons. (unlike if you went thru one of those travel sites)


I know that I've used the travel sites, to get a good route and their plane flight numbers, then when to the actual "direct airline site" and booked it, sometimes.
(I feel the travel site, was easier to use and scan for different airlines, routes, prices, times, layover, etc.) Expedia.com is what I used, in the past, about 80% of the time.