Originally posted by RiceHigh Forget about 3rd party lens and/or superzooms, they only produce inferior results (to the original make and/or shorter range zooms).
Sigh.
I'm sorry, RiceHigh, I try to be courteous here and I generally ignore it when someone says something stupid to me personally, but with all due respect to your estimate of your own authority, I have to say that it is irresponsible to make generalizations like this when you're talking to someone who has admitted they are trying to learn.
I think the "best" lens I own and use now is the Pentax 16-45. I put "best" in quotation marks as it's only best in some sort of geeky, college sophomore meaning of the word "best". Good as it is, for shooting birds at a distance, it's worthless, so it's not "best" in a general way. Anyway, while I acknowledge the excellence of Pentax's better lenses and wish I owned more of them, I'm not such a Pentax chauvinist as to think nobody else in the world can build a decent lens. In fact, if you're going to forget about third party zoom lenses (meaning Sigma and Tamron), then you might very well want to consider forgetting about Pentax altogether, as Sigma and Tamron fill in a lot of holes in the Pentax lens lineup. It's simply wrong to condemn these lenses in such a sweeping fashion.
In addition to the 16-45 (which is not cheap), I have owned three very reasonably priced Pentax zooms - the 18-55, the 50-200 and the 75-300. Decent lenses, all of them. But the Tamron 70-300's pictures are at least as good as the Pentax 75-300's. I think either the Sigma 28-70 f/2.8 or the Tamron 28-75 f/2.8 in its midrange especially is superior to the Pentax kit lens or at least its equal - and the Sigma and Tamron lenses are more versatile lens, offering macro capability and a modest telephoto capability.
I might add that there's no such thing as simply superior or simply inferior. The photographer's goals matter, as do his (or her) budget. If I wanted to shoot snapshots and had a budget of absolutely no more than $650, well, the kit lens would have been perfect. But it was simply useless to me when I started shooting indoor sports and needed a faster lens.
To the original poster: All three of your options are intelligent and viable. Nobody else can really tell you what you should do. If you go with the first option, well, that's a perfectly good way to start. I started that way. I no longer own either of those lenses, having sold them for lenses that I think are better suited to my needs. But the Pentax 50-200 is a very decent lens FOR THE PRICE especially. Let me say again, the fact that I bought the kit lens, then added the 50-200 and the 75-300 and then sold them all, doesn't mean that I made a mistake in the first place. Learning involves making these choices and seeing FOR YOURSELF if you like how they work out. There are folks here who will tell you that they picked up a used lens for $50 that's excellent. But don't take their word for it - see if they are willing to show you some photos that they've taken.
One final point. Your second and third options are the same, except that one uses a Sigma lens, the other, the Tamron. NEITHER of these is a GREAT lens - that's why they're basically giving them away with the camera. But the Tamron 18-200 is a perfectly usable lens, and much more versatile than the Pentax kit lens. I have a bit of experience now both with Sigma and Tamron. I've grown a bit partial to Tamron, in part because I like their lens caps better (really). As far as their lenses are concerned, I think they both make some good stuff, and some very good stuff, and so far as I can tell, nothing they make is junk. I'm only familiar with their recent for-digital offerings.
Good luck.
Will