Cory,
The following is what I have seen in my analysis of Carlisle.
1. I would say there is a demand for apartments especially in the Carlisle Barracks (north Carlisle near route 11) or off the I-81 exits.
2. The higher end apartments definitely go for higher rent and these are located outside of downtown Carlisle (usually near the locations stated in number 1). Another area that can get higher rents is near Dickinson College if you are comfortable with students as renters.
3. The general rent for a 1/1 is roughly $750-$1000 where 2/2 is roughly $900-$1300 with higher end apartments/townhouses on the high side of those ranges. Depending on the location and how nice the apartment you may be able to get slightly above those ranges.
4. North Carlisle (Barracks area) near route 11, close to the I-81 exits, and southwest Carlisle/Dickinson College area are generally the nicest areas of Carlisle. This makes sense due to people working in the Camp Hill, Mechanicsburg, Harrisburg areas but wanting to live somewhere with a lower cost of living and quieter areas.
5. I wouldn't say there is a specific area to avoid within Carlisle but that may be my preference.
I am in no way an expert but this is what I have seen in the Carlisle area. I hope that is helpful and let me know if I can help in any other way going forward.
Jake