I have a some of the Ultimate soldier, and a few of the BBi. I have several Spitfires, P-38's, P-40's, P-47's (both razorback, and bubble top), P-51's, Zero's, 109's, 190's, Corsairs, a couple of Avengers, an F6f, a 262, V-1, F-86, Mig15, F-104, Tomcat, Hornet and my favorite the Dauntless.
The biggest problem for me is their size. I don't have enough room to display more than a few at a time.
At the height of the 1/18th craze I saw a spinach 109 go for more than $800 on the bay. Which is hilarious considering they sold at Wally World for less than forty bucks.