Reliable compared to what? I consider the B5.5 the most repair-prone of that era TDIs. Will a newer one incur more repair events? Hard to say. The NMS Passats have had some post-fix issues, especially the 12-14 ones (the 15s have different engines). Turbos, heater core issues, some injector issues, water pump leaks (not that common) and issues with emissions related components. Good news is everything I mention is covered under the emissions warranty, if you find a car that's still under warranty (most are).
There's less data available on the Touareg, since there are fewer around. What I've heard is the drivetrain is pretty robust, save some folks having driveability complaints post-fix. Just keep in mind the Touareg is a more complex vehicle with more features, so the opportunity for items to break is greater.
Having said all that, I wouldn't hesitate to buy either because both vehicles are superior in some ways to gasoline powered cars out there. But you're not going to have a Toyota or Honda like ownership experience. Odds are, you didn't with your B5.5 either.