When is the best time to plant these, Spring, Summer? NO, Fall! That's right, October is the Ideal month for northern climates, and Even October through January in Southern climates with mild winters. In the north you can cover your beds with a few inches of mulch or straw to save them from freezing. Definitely check with who you are ordering your onions from though, some only do well in the north while others only do well in the south.
Look into popular onion types like Walla Walla, Yellow Spanish or Vidalia. The most common ones are Red, Yellow and White... those are easiest to find.
There are also MANY types of garlic to chose from. Again, check which ones are best for your climate. They are seperated into groups such as soft neck and hard neck varieties. There is also Elephant garlic, which isn't really garlic but related to Leeks. They do grow like, look like and taste like a milder garlic. (This is what I am planting for my garlic bed this fall.)
Here are my bulbs that came today and will go into their beds this week:
That elephant garlic is almost 1lb by itself and bigger then my fist! Growing these are my choice because cured correctly they can last in storage up to a year when I harvest them.