SIG 220 was designed for the Swiss military in 9mm w a service life of at least 10,000 rounds. Also offered in 45/38 Super.
The 225 was designed for the German Polizei trials in the 70s w a service life of at least 10,000 rounds.
A 226 is a hicap 220. A 228 is a hicap 225 and/or a chopped 226. A 229 is a beefed up 228... 229s have fired over 20,000 rounds OK.
OTOH, Baltimore County PD broke 52 of 1400 SIG 9s, switched to sig pros in 40.
OTOF (foot), Tezas DPS contract specified a service life of 40,000 for frame/slide, and they bought SIGs.
In my experience the SIGs get the reliability nod over the Glocks, but it is close, and both are good enough. The Glocks are more durable.
The last FBI trials were for the 40s and the Glock was the only pistol run through the whole test since it was the apparent winner of the suitability test by a sample group of agents. Other guns have had a more limited T&E and been approved, the SIG is one of them. So is the S&W Sigma (the first 40 approved by the FBI BTW).
The INS/Border Patrol did a head to head shoot off with Glock, SIG, Ruger, S&W, Beretta, and the Beretta won. The SIG was an approved option, the Glock is not.
The DEA tested and approved the SIG, Glock, and HK compacts.
The HK compacts did so well, the INS/BP bought 2000 of them for plainclothes agents, passing over the optional SIG (and Glock again).
Lottsa good guns out there. Get the one you like/shoot best, don't worry too much about who else uses/likes it, or why/why not.