I used Baby Bliss by Jo Ryan (sitting on my bed side table right now and I have regularly referred to it across the last 18 mths).
It is a bit more relaxed than SOS and a offers a bit more structured routines than Baby Love IMO.
Jo is Aussie and does regular phone or in person seminars which are great - her phone session on 4 mth sleep regression and cat napping was a life saver for us. You can also get her or one of her team out to your house if you are really having trouble and need more intensive help. I really loved knowing that was a back up if I needed it.
I agree to get them all second hand and figure out what works for you and your bub.