I only have one that I use regularly and I use it way more than going manual.
However, I noticed that if I used the vibe multiple days in a row and then my ex as of a day ago *cries* would go down on me I wouldn't cum as fast as I would when he would go down on me before I got my toys. I made an educated guess that my clit was getting used to the harder, faster, more direct stimulation of vibration as opposed to hands and tongues so I now make an effort to give the vibe a break and do it manually. Maybe two out of 5 times? Problem solved.