The best adult diapers for wearing 24/7 are the Mega Max Diapers from Northshore.com or Northshore Supremes.
Abuniverse also sells good absorbent diapers for adults such as the Abu Little Pawz, or even plain white diapers that are plastic backed as well and very absorbent.
All the diapers from Abuniverse are very absorbent and good for everyday wear and can hold up all day without needing to change the diaper.
If you're looking for a thinner and more discrete adult disposable diaper then try attends poly backed from healthykin which are around $30.00 per case of 96 diapers which is a decent deal.