We went last year and had a really lovely time. We specifically wanted to go to Quinta because of the golf and proximity to airport. Martinhal was nice - is not a complex specifically built for them, was something else they took over so last year they hadn't completed the refurbishment of all the villas, probably done by now. Many are privately owned. My children enjoyed the communal pool area but beyond that didn't use many of their facilities - the creche looked more like somewhere for smaller kids than my 6 and 8 yr olds. They could have done with a playground. We have not been to the other Martinhal at Sagres so can't compare. We ate in a bit (supermarket on site not great, go into Quinta or Almancil (best one in Almancil) and also went out to restaurants. We hired a car. We had however been to Quinta before so knew where we were going if you see what I mean.
Quinta is an expensive resort. So if you want something cheaper, maybe look further along the coast. Otherwise some family friends who have a place there say that the Four Seasons complex has more activities for the children. Or you could rent a villa and use the facilities in the resort.