Dual Beam Transducer or Dual Frequency transducer

[reel escape]

Just bought Garmins 545s GPS/ Chartplotter which also has sonar and don't know which transducer to buy, I have a lowrance 102c which works great for shallow water fishing/jigging. I can buy either a dual beam or a dual frequency transducer, the main purpose of the second sonar would be used for trolling so I know the dual frequency is probably the right choice. Just wondering if anyone runs the dual beam and if it works for trolling and reads the downrigger balls? Thanks for any input.

[ray koziatek]

dual freq.