It really depends on the mood I'm in. Sometimes I just use my trusty rabbit style vibrator. Other times, I'll also use a vibrating anal probe. Lately, I will sometimes use a dildo with a bullet type vibe for clitoral stimulation.
I usually use two or three, sometimes more, during masturbation as well as PIV sex I will usually have a plug in my butt and I will use both a vibe and a dil. Depends on how much time I (we) have to play.....
Usually, just one. Once in a while I'll use more than one, but those occasions are few and far between. Usually I pretty much just want to get off and have some fun, instead of hauling open the whole toy box!
I am partial to using just one... It simplifies the whole process, especially cleanup.
However, I may occasionally wear a butt plug for a number of hours and later conclude with a dildo. Variety can be nice.