OP said he "doesn't play enough to take advantage of PokerStars VIP rewards program." So the same applies to Party, which also has his own VIP program (bit worse than PS).
All those sites/networks (Ongame, iPoker, Entraction, Merge) TOGETHER have less traffic than PokerStars alone. You shouldn't even compare
A good thing is that if you register on all these sites, you (almost) don't lose any value with "not-clearing" first deposit bonus in time.
Ongame, iPoker and Merge have either "deductible" SignUp bonus from rakeback, or % is the same. Only Entraction has FDB with no correlation to rakeback, but it releases in increments, so you don't lose much anyway.
That's why you can play on all these sites simultaneously. Even if you don't find a proper table for a week on Ongame, you don't lose any value.