As a rule, a filter should be as close to the radio as possible while the preamp as close to the antenna as possible. The reason for this is you will want to filter out not only what is picked up by the antenna, but also any junk picked up by the feed line as well.
The preamp works best with maximum signal levels to amplify. If you don't place it at the antenna the signal you're trying to amplify will start out smaller (and with more noise) and often there may not be enough signal left for the preamp to amplify. A preamp will not only amplify the signal, but also the noise. If you place it away from the antenna you'll get an increase in the relative noise level.
That said, the preamp will also amplify what signals may be filtered out by the filter and therefore cause the filter to be less useful. Remember that an antenna is not just the antenna itself, but an entire system (that you're adding parts to with the preamp and filter). You should tune the antenna as a system and not as individual parts and be prepared to make adjustments as you go. It might be best to place the filter at the antenna ahead of the preamp as well, but only trying different combinations will say for certain what will actually work best in YOUR installation.
I'm sorry that this gives you some conflicting answers, but that's just how an antenna system works. There's not a single hard-and-fast answer to how to make it work best everywhere. One thing you can take away from this is that the middle of the feed line isn't the best place for either.