There is no easy answer to this question so i will ask you a questions.

What type of bets do you like to place(racing,sports,win betting,exotics)?

If the $100-$150 incentives are appealing to you, I suggest you need to take a closer look as to why you bet at all.

Its a bit like them Lotto players who only play when there is a jackpot.
They ain't fair dinkum about their lottery playing.

You sound like you have decided that you have lost before you have even started.

If the agency offer Odds on the events you wish to participate in, then they are suitable candidates.
Open account with any of them, and if you have dramas, take your money elsewhere.
The best way of finding the most suitable for you is to shop around.

Its bit like supermarket.
They all sell pretty much the same groceries.
But we all usually go to our usual one after having tried a few.