Of the two, the Glock would be my choice.
1. The Glock 21s (either SF or Gen 4) seem to be so far unaffected by the problems encountered in other Glocks since the introduction of the Gen 4.
2. SIGs have suffered from quality problems, particularly with small parts, in the last few years. I believe their high cost is no longer justified.
3. The .45 version of the P220 has historically been the least durable and reliable member of the P22X family.
4. I don't see any compelling reason to choose a DA/SA gun over a striker-fired one when starting from a clean slate.
The S&W M&P 45 is also worth considering.