The operator is the key not the software (from a stiffing the players point of view). Any of the big-books will be fine for your casino. If they have money to pay your sports winnings, they will have money to pay your casino.
Now the games, that's a whole different matter!
Of the sports book-software providers, I personally recon IQL has the best looking games. However, they are not a patch on a specialist casino-only software provider's games - casino software from an IQL or an Extension or a DGS just has too few games which are not interesting enough for me.
Important to separate games and backend's...play with someone you know and trust and you will be fine.