Hi Kevin,
The kinetis K series such as K64 supports both JTAG and SWD debug interfaces.
Having said that, both P&E Multilinks and Segger J-Link working great, as well as I-jet if you are using IAR; I'd say to go on with what you have already, if any.
Personally I am fine with J-Link but as mentioned also Universal Multilink is really OK.
I don't know what IDE you are using, in case it is KDS let me add that KDS supports obviously P&E Multilinks (including P&E OpenSDAv1), Segger J-Link (OpenSDAv1 and OpenSDAv2) and OpenOCD with CMSIS-DAP (both OpenSDAv1 and OpenSDAv2).
You can see HERE how to setup debug configurations with recommended settings.
Hope that helps,
Antonio