What would be more effective, having individual sales persons handling individual territories or having them work in teams?

It will depend on the type of Business & its Range.

Being Said If individual person individual territories is much better considering that it can be easily tracked the sales in each area vs total market capacity and can be discussed with the person in charge of that territory. If all the sales persons work for all territory may become messy.

.  Eventhough there will be tough time tough time for sales person territory with not much market potential . Company can Easily track the sales data & rectify things accordingly. 

Individual Sales person with common back office is better .

If all team working for all area; then its better split the  clients between sales person  like 1 or 2 sales person meeting the specific list of clients. 

The advantage of individual sales persons is that helps cut or reduce related costs such as salaries, allowances or travel expenses which are evident in using sales teams while the advantages of using sales teams include; timely management & execution of duties, wide range courage of markets, better service deliver, quick resolution of problems for instance they can seat & discus what to do-sometimes two heads are better than one, fast tracking of transactions, better market research & information richness since almost every member in the teams brings something on the table etc.