The engines or hearts of all modular synthesizers are definetely the VCO's. As main sound source for your patches it seems you never have enough of them.
I own 5 VCO's at the moment, One A-111 High End VCO plus four A-110 Standard VCO's. Ideal for stacking layers of waveforms to make extra- fat sounds, and also very useable for multiple A-100 melodylines
The A-111 is the one i use most because of its extended possibilities.
This VCO has an extended frequency range, improved waveforms, FM and Soft Sync inputs plus an extra fine-tune-controller. Ideal for controllerfreaks like me.
It produces sine, triangle, pulse and sawtooth waveforms, which are all derived from the triangle oscillator, what does make it hard to produce perfect sine-waves ( but a little better as the A-110's sine wave )
One of the best things is that all 4 waveforms are all simultanously available at the outputs for your mixing pleasure.
The much cheaper A-110 has less controls and is based on a sawtooth oscillator. All