SIG is a Swiss company. "Swiss" is right in the name: Schweizerische Industrie Gesellschaft ("Swiss Industrial Society"). "SIG Sauer" was a joint Swiss/Germany project originally. Things have changed over the years and in 2000 the firearms side of the company split between "SIG Arms" (the German/American side) and "Swiss Arms".
Anyway... the two main pistols I am shooting these days are the GLOCK 19 and the SIG 228, so I suppose I am pretty well qualified to answer your question. I also have the SIG 229 and 239, and I used to have a GLOCk 17 as well.
Both are great. Both are very accurate. Both are very reliable. That isn't going to help you much though.
The big differences for me are: (1) trigger, (2) trigger reset, and (3) bore axis.
The GLOCKs have a much shorter trigger reset than classic SIGs. The SIG SRT trigger has changed the game for SIG, but many new guns still have the original trigger - and of course the hundreds of thousands of SIGs produced over the years have it.
You can get used to anything, but if you are used to shooting a short reset trigger (1911, GLOCK) you will not enjoy switching to a longer reset. On the other hand, if longer reset is what you are used to, this becomes a non-factor - as you brain does not think of the reset as "long".
The trigger on SIGs has a much finer break point than a GLOCk. That doesn't necessarily mean SIGs shoot better, but it does mean you have to learn how to shoot a GLOCK trigger to have success with it. Don't finesse a GLOCK trigger. Pull it. The traditional shooting advice about slowly "squeeze, don't pull" - I don't believe this applies to GLOCK. Learn to shoot the GLOCK trigger properly and you will stop believing the "GLOCK are not accurate" myth. A solid grip and proper trigger technique and GLOCKs are very, very accurate.
Bore axis: classic SIGs sit higher in the hand. Extend your trigger finger while holding the pistol. On a SIG your finger will be completely under the barrel. On a GLOCK your finger will be closer to the level the barrel is on (I'm not sure if this makes sense without pictures... hopefully it does). Like the trigger issue, you can overcome any disadvantage this may present with practice. In 9mm it doesn't make much difference (if any) anyway, as recoil is easily controllable. Higher bore axis.. shooting +P .45 ACP's or something like that, the "get back on target" speed is probably going to suffer a bit for most shooters.
My view... SIGs seem to be easier for new shooters to get good results with. I see so many people buying GLOCKs as their first pistol and they really struggle with it. I was the same way. Took me years of shooting before I came back to GLOCK and learned to love them. SIGs are awesome guns and I will always own and shoot SIG. The 228 in particular is just plain cool. However, the more skill and experience I have developed with pistol shooting the more I see the appeal of the GLOCK. I really believe it is hard to beat the GLOCK on a "best of all worlds"/"lowest common denominator" kind of basis: cheap, tough, accurate, simple, reliable, common, tons of factory and aftermarket parts and accessories. Took me a few years to get there in my own mind... but GLOCK didn't take over the pistol market by accident.
Having said that, SIGs rock and I love shooting them. They feel "quality" and many people think they feel more like a "real gun" vs. polymer frame gun. GLOCK has a lot to offer though. If I could only have one pistol (perish the though), it would be a GLOCK 19... but I would be real close with the 228 and 229.