If the homes value will be increased substantially by applying new siding, that would be your best option if it is vinyl or aluminum siding. Also, color matching due to fading may be an issue so take this into consideration when deciding. If it is wood siding, then repairing it may be a better option. Get prices on both and an estimate of the increased property value and then decide.
Repair is always the most cost effective method, but this is contingent on many items.
Repair is always the most cost effective method, but this is contingent on many items such as age, bugs, water damage and the like.
Repair will be cheaper but you also have to remember that unless the existing siding is only 1-2 years old its going to be almost impossible to get an exact match. Also you could be losing insulation value from your walls if your previous installer didn’t install foam board or house wrap and you should always try to get a closed cell material as it does not retain any moisture or water. So the answer to your question is really based on how much the home value will increase and the length of time you plan to stay and the contractor you choose to do the work
Repairing is going to be more cost effective. One option if you have damaged siding that you can’t match would be to do some type of a design feature in the front (perhaps a hardboard siding in the front) and use that siding to repair the other elevations. Depending upon the age and quality of the siding on your home south facing portions of the siding might be more faded than the north facing portions.