2 Inv osc
I build this osc with 2 inv, but more can be used. You can also use different chips - actual inv or other digital gates that can be hooked up to form an inv. Generally I use a 4011 (quad 2 input NAND) because I like a signal for pitch and a signal to control "looping" with a 4016. I can get everything I want out of one IC while using up all pins. Using a 4069 (Hex Inv) would leave unused pins (which could be utilized for more if I really want to), and be a larger package taking up more space. I try to minimize the size of my circuit to fit everything (pcb w/components and pots, switches, etc) inside of the toy.
The minimum value I use on R1 is 1K and R2 is 100K because more can always be added. Cap value and type I experiment with.