The new 1769-L24xx controllers don't have a serial port, so the old "Modbus using ASCII commands" method won't work.
None of the ControlLogix family controllers have implemented Modbus on the built-in ports the way the MicroLogix and SLC controllers have.
Prosoft is still the gold standard for Modbus networking with any A-B controller. I know they're working on the development of a POINT I/O module for Modbus RTU protocol, but I think it's still in the preliminary stages of development.
There are alternatives to Prosoft; I have an inexpensive GridConnect Modbus RTU Master on my desk now. HMS Fieldbus and Real Time Automation would be my first two choices behind Prosoft for a Modbus RTU interface to ControlLogix or CompactLogix.
If you are not constrained by time, performance, or stability requirements, you can go afield and look at other interfaces. If it has to work the first time, use Prosoft.