Not the best, but the best for you
Be wary of universal "best pillar 3" rankings: the right choice depends on your age, investment horizon, risk tolerance and need for flexibility. A young worker and someone near retirement don't share the same "best" 3a. The question isn't "which is best?" but "which is best for my situation?".
Bank, insurance or funds
Bank 3a is flexible (free contributions, low fees) and can be invested in funds for better long-term returns. Insurance 3a combines saving with cover (death, disability) but with fees and a rigid commitment. For most savers, a bank 3a in funds is most efficient; insurance makes sense mainly when you genuinely need the cover.
The criteria that really matter
Look above all at fees (a 3a fund's management cost / TER erodes returns over 30 years), the fund's equity share (higher = more potential and volatility), flexibility (free contributions, transferable), and the absence of binding commitment. Over a long horizon, low fees and good allocation matter far more than a headline tenth-of-a-percent return.