Generally speaking, "max bet" means you need to play the maximum number of lines and the maximum number of coins per line [if applicable], but not usually at the maximum coin size.
Microgaming's progressives all have a fixed coin size, except for Megaspin Major Millions which you can adjust. But I'm not sure how that works - if I were playing max bet with maximum coin size and someone won the entire jackpot with a max bet of the minimum coin size I would probably feel a bit ripped off, so I am guessing that the smaller coin sizes would result in a proportionate amount of the jackpot if won. Otherwise, why would anyone risk playing with a larger coin size?
With Wagerlogic's Rapid Fire and Marvel jackpots, the larger your bet per spin the greater a chance you have of hitting one of them. These slots don't bother with the concept of coins and coin sizes, just a bet per line, so you need to make sure that you bet on all of the lines. I have hit the Hero jackpot frequently with a total bet size of $2.25 on the 9-line Marvel slots.
Realtime Gaming's random jackpots are a bit of a mystery; the game rules don't indicate if a larger bet size increases your chances of hitting one, but it probably does.
