in my experience some cycling shorts have a more 'technical' pad than others. They tend to be more expensive than those with a more basic pad.
The more technical the pad, the more expensive they will be.
They do/claim to do (delete as appropriate according to how cynical you are) on how to get the pad to stay in place when cycling, they claim that a more technical pad will perform better than a one piece pad when both legs are moving independently of one another. Again, to what extent you believe those claims is another matter.
What i will say though is in my experience those with a more technical pad seem to be better on a narrow race saddle, while those with a more basic pad seem to be 'better' (read: just as good, therefore better value 'cos they're cheaper) on a wider saddle like a brooks.
Examples of shorts with a technical pad: Assos, de-marchi
Examples of more 'basic' shorts: endura, trek.
Personal recommendations: Ive got some trek ones which were £26 and they are absolutely brilliant on the brooks, not too bad on the race saddle either. To such an extent i will usually reach for them first on an audax.
De marchi - they were quite expensive, fairly technical pad that seems to work quite well as they are always comfy after a long ride on a race saddle. Can't seem to find anyhwere that stocks them though now?
Giordana: fairly 'small' sized, but don't order one size larger to compensate. Small is good. Seems to be a bit of a stretch to get them on, but they stay in place better than any others, which makes them very comfy.
DHB: don't like them personally. Got some which are actually not bad when they're in position, but they 'ruck up' easily and aren't that comfy off the bike as they aren't the right shape. Some newer/more high end ones may be ok though, i know wiggle do improve them and bring out new ones fairly often.
Assos: brilliant but if anything slightly large sized, if in doubt get one size smaller. I have some in large and they just aren't tight enough to stay in place enough for road riding.