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.
That's pretty much what happened to me on my VG. Got to 28, got bored. There's really no thought process to tanking on a VG. It feels like you're just hitting things as they come off cooldown and peppering hammer shots in between to keep your ammo up.
Shadows/Assassins are good. If you wanted to play one of them as a tank though I'd probably start out speccing in infiltration/deception as opposed to the tanking tree until the 20s or 30s for a couple reasons.
1. The tanking tree for shadows/assassins don't really seem to give anything substantial until the 20s and 30s. In the early levels you don't really have the tools to make anything feel efficient or worthwhile until you get talents like energize or harnessed darkness (don't recall the name of the talents for shadows), and since you aren't specced into deception maul isn't going to be efficient enough to use, so you end up mainly spamming thrash most of the time which is just boring.
2. You start off with a tanking companion and don't get a new one till your mid 20s (assassins get a DPS companion next and I think shadows get their healer?), so I say take advantage of using your companion to tank at least until then and spec deception/infiltration to stab the mob in the back while solo questing. You can still tank heroics and flashpoints by switching to your tanking form as that's all you really need at low levels anyway, then you can respec later. I will say though, even if you do spec tank right off the bat sins and shadows feel the squishiest of all the tanks, mainly from not having any defensive cooldowns early on.
Personally I'm liking my Guardian a lot. I really like their resource system even though people say it's the most complex. It also feels more dynamic than either VG or Shadow, but shadow gets funner later on, it's just kind of a late bloomer. Even if Guardians might be the weakest tanks atm (or at least the hardest to be good with) that just adds extra depth and challenge to it, and overcoming adversity is half the fun.