More than anything else, an auto-titrating machine will blow the LOWEST pressure that you require to maintain patency of your airway, throughout the night and as such, generally improves compliance (usage) significantly.
APAPs are not thought to be a good idea in certain cases, such as those with a history of heart failure for which the increased pressures that an APAP may get to may aggravate the occurence of central apneas or Cheyne-Stokes respiration (CSR) that oftern accompanies heart failure. For those, ResMed's new VPAP ADAPT ASV or Respironics' HeartPAP may be better choices.
For the rest of us, auto-titrating machines have provided greater comfort and therefore, more complaince in most cases, though there are those that will continue to sleep better with constant pressure from a CPAP. BTW, every model APAP can be set to run in CPAP mode. CPAPs CAN'T be set to run in APAP mode, however.
There are dramatic differences though, in the ways that APAPs from the different manufacturers perform, however. So, you will find that you'll do better on one brand or the other, and you OUGHT to do what you can to at lkeast try the variety of different brands until you find the one that works best for you.
For example, REMStar Autos are universally revered here. But they are NOT for everyone. They tend to be slower in responding to SDB events, and so, these events can cause arousals. ResMeds are very quick and aggressive in their response, but this aggressive attack tends to arouse some folks resulting in poorer sleep. So, make sure that you insist that you be given the opportunity to try them out to find the one that works best for you, if at all possible.
Hope this helps.