Jugg tanks are the most sturdy but have the lowest threat
Assassin tanks are not quite as sturdy as Juggs but have the highest threat (because of their high damage)
PT tanks are somewhere in between
Most of that isn't true (Guard/Jugg tanks do have the worst threat and Shad/Sins have the best, but it's not for the reasons you indicated).
Shadows actually require the least outside healing of all of the tanks and have the best overall survivability. The only way this isn't true is if said Shadow tank has no idea what they're doing. The issue that many people have is that Shadows have the least stable damage profile. What this means is that damage coming at a Shadow tank will be very spiky but that they will end up needing to be healed the least (which is a combination of their self healing as well as less reliance on DR which always works for def/shield/abs which have chances to work). Also, they've got the best threat not because they've got the best damage; they've got the best threat because they've got good damage *and* have a number of high threat abilities that are used *a lot* to deal a lot of damage (Project gets 15% bonus threat, Slow Time and Force Breach are both high threat abilities).
Guard/Jugg tanks are the de facto worst threat generators and damage dealers. There's no question about it whatsoever. They're also the hardest tanks to get proficient with (Shadows are the hardest to get truly amazing at, but there's a difference between proficient and amazing and you seem to be asking about proficiency more than amazitude) because of said threat generation and the most complex resource maintenance. For survivability, they're actually in the middle of Shadows and VGs: they have a more stable damage profile than Shadows but more overall damage taken and vice versa VGs.
VG/PTs are the simple tanks: they've almost entirely devoted to passive mitigation (meaning you don't have to push buttons to keep yourself alive) and very simple attack priority (I generally call them the faceroll tank because you can really get away with just smashing your keyboard and playing one pretty effectively). Their threat is decent but not amazing (better than Guardian, worse than Shadow) and, for survivability, they'll end up taking the most damage of all of the tanks but have the single most stable damage profile of all of the tanks.
If you're not really looking for something for absolute top tier performance and don't really care too much about learning the ins and outs of tanking, I'd recommend going with a VG/PT tank: it's simple and effective. The only problem with it might be that you find it too boring to play and just get tired of it.