SLH-DSA aka SPHINCS+ is the most conservative choice (i.e. they are all secure against currently-known attacks, but SLH-DSA is less likely to be broken later),

SLH-DSA aka SPHINCS+ is the most conservative choice (i.e. they are all secure against currently-known attacks, but SLH-DSA is less likely to be broken later), but it is slow (at least several milliseconds to sign) and produces large sigs (>= 7.8kB). This means that it may not be suitable for all applications. Dilithium is faster but less conservative, harder to implement securely, and produces medium sigs. FALCON is even harder to implement securely, faster to verify and produces smaller sigs, though still much larger than classical systems. IMHO this choice was questionable, in that its advantages overlap too heavily with Dilithium to be worth another standard, but NIST apparently felt otherwise.