Currently using a TP-Link WDR3600 running DD-WRT and two Gigaset N300s. DD-WRT doesn't seem to have a SIP ALG, so nothing to turn off. Not got STUN enabled on the N300.
In the past I've used a variety of Drayteks, mostly the V models, with Linksys/Cisco ATA, then the onboard VOIP on the router, then with Gigset N300. I set up one of the cheap Cicso ATAs for my mother-in-law so she can call my sister-in-law in Australia, and that seems to work fine with her Talktalk supplied Huawei (not sure of model number).