I find that ACR is softer than Stars. It also depends upon time of day & what is happening on sites.
ie. During times 00:00 to 09:00 GMT, USA players are off work & playing. << These are the players that one would hope to target. Days of the week make a far greater difference as well (evenings on Friday being the best, Saturday is good too... ie. 17:00 ET > 23:59 ET (GMT -7).
other things like promos sites are offering can affect the player pool significantly
ie. Lately on
partypoker they were holding a promo where you get to click on a card if you were dealt AK, AQ while on FastForward tables at 10nl or higher. This actually seems to bring out many players to those tables who don't normally play that format (& it shows!). Far juicier than normal (normally it is infested with aggressive regs.,.. some of them good, many of them not so good)
SportsBetting/ Betonline seems to be the softest of all sites I have had recent experience on. Unfortunately(?) I have a very small
bankroll on there so I have not played very much but from the limited time I have been on there, it has many bad players there. I've considered depositing more on there but you get hit with big fees, poor currency conversion rates & is also a PIA for withdrawals (from what I hear... I have never WD'd $'s from that site).
888Poker tables are very soft as well... but small player pool there.
And I'm not sure if any of them even have full ring tables these days.