Hi, it depends. If your are looking for a phone with single line or directory number and MWI go for IP Phone 7911.
For additional capabilities (midrange phones) like multiline, MWI, Large pixel-based displays, Integrated switches, Built-in headsets and high-quality speakerphones, go for phoe 7940/42 or 7960/62.
For a detailed list of features per phone model, you can go to the data sheets of the IP Phone 7900 Series products.
All the best
David.