HP vs AIX Memory

I have 2 boxes one running AIX 5.3 and the other running HP 11.31. Both systems have the same application running but HP seems to be using more memory than AIX by almost double. I have to use 2 different methods because both machines have different backend software to look at memory. What is the best method to see side by side memory usage on the system and per process

Granted if i look at glance on hp see say 13gb free but if i look at nmon on AIX i see 636mb free. Which way is the correct method?

Both are correct, so how do you come to the conclusion HP uses more memory than AIX by double?

Do both boxes have the same available system memory? I see a lot of services seem to take advantage of having more memory and allocate more ahead of time when there is plenty available. top or vmstat avail on AIX?