Ha, I suppose there's two sides to every story...
I have four guys, and keep
three types of food (Beef*/Foul/Sea) out for them 24/7. They alternate between the flavors, but seem to prefer more Beef in the cold months, and the others during the summer.
All were raised from Puppies with this regimen, and I don't have any issues with Resource Guarding. In fact, I think I have the most polite dogs ever, when it comes to sharing their food. Probably because of the abundance.
This approach is not very popular here on the forum (lots of ways I do things aren't) but it has worked well for me, and, it's apparent that my guys like the variety. I think the most important issue is, that you provide them with a high quality diet, regardless of flavor or consistency.
You can find some very highly rated foods here...
Dog Food Reviews and Ratings | Dog Food Advisor
* = Actually I alternate the Beef with Lamb and Pork through the winter months, and have the Foul and Sea available to them throughout the year.