You can almost double the money by going direct with the owner/operator but if you do not have the contacts or know someone looking then a company like ACASS might be a good way to get your feet wet in the contract world. Once out in the field you can make contacts.
Things to be careful about ACASS are that they will try to low ball you on money, almost always. They play games like offering you one rate then you find out later that your copilot is making $2-3,000 more a month than you are and they expect you to be happy with this while you are taking the responsibility and doing all the paperwork. The market is very short of experienced pilots and if they need you at the last minute will pay whatever is needed. If the copilot signs up late and is hard nosed about money its not unusual for them to be paid more than the Captain. Fair? Not for most of us.
One thing about ACASS is that if its in the contract that you sign with them, they will do what is there. They pay their bills (but have been late with some pilots lately I have heard) and expenses. They do try to get you to put all expenses on your personal credit card, and if this is a hassle then simply refuse. Tell them you are maxed out and if they want you to fly then they get to pre-pay the hotels. They do it with some crews but only after making a lot of noise. They want you to put your expenses in every 2 weeks. Do it every week otherwise you get to pay the interest on the credit card and they make money on it.
There is another contract company in Western Canada and stay away from it. Its in Calgary and they have hundreds of pilots going after them for not paying their salary after they were on duty overseas for 4-6 weeks.
If you finish your contract and turn the expenses in with ACASS you will get your money, something that cannot be said about the company in Western Canada at this time.
CD