Extra benefits of Solitaire over PPS
Can use SQ F lounge regardless of airline flying with or class of travel.
Partner supplementary solitaire card.
Higher priority for waitlist (yes I've already used this successfully).
Higher priority for op-ups (I dont think its a coincidence in around 100 flights before solitaire no op-ups, but already 2 since then).
Use first class check in for SQ even if flying Y.