You can go MOM website, they published quarterly list of agencies, on their maids passing exam rate, maid changing employer rates.
There is no really "good" agency, all depend on luck, but I know some agency allow free replacement within a year, some dont't (like Nation, I heard they dont't allow replacement, meaning everytime you change, they charged you again).
I got a transfer maid last Sep cos my old maid of 6 yrs wanted to go back to get marry, I paid my agent $268, unlimited replacement within a yr. But you have to take note, every time you chg maid, the insurace only refund you 30%. Also, MOM may select you for questioning and interview if you change maid more than 4 times in 12 months.
My advise, try not to get transfer maids or maids that have come to Sg before. I took 2 tfr maids, both cannot make it, until i choose one fresh from indo, got 5 yrs experience at saudi, finally ok. She so far wk with us 2 mths .
So far, no agency to recommend, you must go see their biodata, see whether they fullfil your requirements.