The reason I ask is because if one plays clean, then in many respects a reverb pedal in front of the amp won't behave all that differently from an amp with built-in reverb. The amp's tone controls will shape the reverb tone as well as the guitar tone. If, on the other hand, one expects to punish the amp's front end a bit then hitting it with a reverbed signal may not elicit the desired overdrive tone from the amp. In those instances, it is preferred to tap the amp's preamp stage at some point, feed a parallel path to reverb of some kind, and blend the reverb in with the amp's overdrive sound.
The big qualification there is that not all desirable amp sounds come from the preamp stage, especially if it is a non-master-vol amp. In many of those cases, the magic is more from the power stage, such that it makes not a bit of difference whether one's reverb is a pedal ahead of the amp's input jack or a spring pan inside the amp; you'd still be trying to push the power stage with a reverbed signal one way or the other.
All in all - and this is entirely subject to your preferences - my sense is that the most pragmatic solution is to get your overdrive from a pedal, feed that to a reverb pedal, and try to run the amp as clean as possible. BUt that's me, and ther are always plenty of interesting and musically-valid exceptions to the rule.