I always considered the "level system" of 888 the most player-friendly, especially when you like to play
freerolls.
When I used to play there, there were certain freerolls up to 10000$, depending on your level in their bonus system.
You would level up by either reaching a different goal every day, like winning with a hand they had chosen for the day or by spending cash for tournament buy-ins or in cash games (also for sports betting and the casino).
I managed to reach level 40 and thus was allowed to participate in a weekly freeroll for a total prize money of 2000$ (there were also other freerolls you could register for, like a 1000$ freeroll 3 times a week for lower levels and many more), even though I only deposited about 50$ once.
Additionally, there were daily tasks, for example winning with a certain hand in a cash game, like A-K. In case you would manage to do so, you'd receive direct cash-back.
Last but not least, there were promotions with changing freerolls from time to time, which you were able to take part in with tickets.
There were a few tickets given to you at the beginning of the promotion and you could earn more tickets - again - by completing tasks as mentioned before.
In the moment I'm playing and Pokerstars and GG and I haven't seen any promotions nearly as rewarding as there is on 888 (in case they haven't changed it up too much).