There are a few points about pad sounds.
There are two types of pad. One is a smoother much less complicated sound but still moving in a slight liquid / detuned manner. These were often generated by synths like Prophet, Oberheim etc. Brass sounding saw waves going through nice filters set to cut off quite low and some filter resonance added for some extra colour.
Other pad sounds can be very layered, complex and dense. These might sound great on their own and are probably best used in that way. They can distract under a vocal and guitar etc.. Absynth is good for these types of sounds.
Two simpler pads can be layered to create a wider slightly more complex sound. Then with just a hint of something like
Dimension D you have got a pad sound to die for. Wider stereo pads are good for staying out of the way of material panned centre. A mono compatibility check is important though to see how they sound collapsed down to mono.
The more the complex the rest of the music is you are trying to put a pad under, the harder it is to hear. Keep the music very simple and uncluttered. Should be a big black backdrop before the pad is added. Even when there is space the best pads are often the simpler sounding ones and turned down low as well. Maximum illusion minimum voltage.
Pads don't have to be drenched in reverb to sound good either. They can be dry as well. Delays are sometimes interesting on them. The ADSR of the volume envelope is critical to getting the pad to fit your music perfectly. I have found very slight amounts of distortion can make a pad sound fantastic.
Watch out for some serious bottom end coming from some instruments. The pad might need some HPF to thin out and tame the bottom end. Especially if there is a bass player present. Let them create the bottom end and it will be more rhythmical.
Use Roland
Dimension D where you can!
It is perfect for adding depth and increased liquid movement but not distracting. You have a lot of control over various aspects of the liquid movement especially the plugin.
Analog synths making the pad sounds used to be king in this area but there are a plethora of VST's that can do it too.
But most of all the most important thing is to play them right when they are most needed so they have the most emotional impact. That is when they work best. Pad voicings are important too. Sometimes root and fifth is all you need.
(Even one note at times!) The other chord tones will setup a different vibe. You have to be careful how many chord colours you are going to drop into them too. They can over power and clutter if abused.