The only problem I have with PTWs is their cost. I have a dozen of different AEGs and GBBRs but stopped using them after I got a PTW. Yes, the parts are more expensive but they are way easier to maintain, way more accurate and give you somewhat of a recoil feeling as opposed to an AEG. The only problem I have had so far was the broken motors which had to be sent to TAC. But once he moded them nothing compares anymore. TAC has a facebook group "Tackleberry's Systema PTW User Group" https://www.facebook.com/groups/180170635373712/
where you can find out more from PTW users.
Otherwise I like the AEGs which allow you to change the spring without having to open up the gearbox.