Regarding deals, ask recent regular posters of the
Pokerhost thread (an O/8 forum regposter spimp13 also plays there), I have little knowledge of the Merge network (was at Host as a ROW resident back when there was 35% RB instead of the terrible VIP program whose top tier is invitation-only
). Carbon has bigger promotions than Sportsbook too.
However, if I remember right, there's segregation of player pools on Merge - some tables are seen from Carbon / Aced + Host only, and some from PlayersOnly / Sportsbook only, can't comment on which pool is better, or maybe PLO is not segregated.