I would try to have both, why
It’s hard to compare Novation Peak vs A4:
- 3-VCO vs a 2-VCO synth
- 1-VCF vs a 2-VCF synth
- 8-voice vs 4 voice polyphony
- mono-timbral vs multitimbral
Just to point out some important differences of the synth engines.
Both have a wealth of different modulation and crossmodulation capabilites. Maybe that the A4 has more options, even if we do not consider the sequencer but IMO the audio-modulations are more interesting on the PEAK.
- FM Osc 1 -> osc 2, osc 2 -> osc 3, osc 3 -> osc 1 and noise -> osc 1
- Osc 3 -> filter cutoff frequency
- Noise -> filter cutoff frequency
A strength of all Elektron devices is the integrated sequencer, which makes the A4 to four independant synths.
At the end it depends on personal taste, sound-design goals, the music style, and workflow, which of the both could fit better to ones needs … if only one can be afforded