Well I guess that LFO with knobs are much more performative, but this is a matter of taste.
I have a Doepfer A-145-4 in each rack.

Also, for you system, considering a simple VCO to be used for audio rate modulation duties would open many possibilities. I suggest very simple modules such as a Doepfer A-111-3 or an Intellijel Dixie 2+