Best First Lens Choice

There is no best first lens choice. The kit lenses are a great place to start. What's good for you depends on what ends of the G9 zoom you used most. The long focal range zooms involve a lot of compromises, particularly in lower light levels, which may or may not be acceptable to you. Read the reviews for that Tamron lens again and think carefully if that is what you want.

A Canon 18-55 or 18-135 plus a 50/1.8 would cover a lot of ground for the money for a new DSLR user.

This post might be better placed in the Canon EOS forum than in Digital Cameras, since it is Canon-specific.

The Canon 18-135mm lens isn't really that great. I'd suggest the Canon 15-85mm instead, or just the 18-50mm kit lens plus a second lens for telephoto work. The Canon 50-250mm lens is decent, and it's compact and lightweight. These lenses all have IS (image stabilization) too.

On the one hand it's obviously convenient if you can do everything with one lens, but on the other hand you give up a lot in quality when you do that, and it means that your camera is always burdened with a bulky lens even when it doesn't need to be. I suggest instead thinking in terms of a complete system with a small selection of lenses for different purposes. For the new DSLR owner, the 18-50mm kit lens plus the 50-250mm telephoto zoom is a pretty decent way to get started.

Thanks to both of you!
I really like the idea of the 15-85. It's not far at the long end from my G9, and I like wider angle at the short end.
Paul

Tamron 18-200/3.5-6.3 lacks image stabilization. Tamron 18-270/3.5-6.3 with image stabilization (called VR) is a fairly bad lens that, in all versions, underperforms some inexpensive superzoom bridge cameras at base ISO.

Aside from the Canon 15-85/3.5-5.6 IS, the Sigma 17-70/2.8-4 OS is worth considering. It costs a bit less and is also very good optically, and faster. Of course if you go with Sigma, you could buy a Nikon body.

It all depends on what you like to shoot, but a zoom in the 17-70 range could become handy...

Tamron's 18-250 performed better than their 18-200 in several reviews. It was good enough that Pentax even licensed the design and made their own version. I don't know much about the 18-270, with or without image stabilization, but the 18-250 wasn't that bad of a lens when you consider its size and capabilities. If the the size and capabilities of the 18-200 appeal to you, I'd suggest looking for the 18-250 instead. Most reviewers have said it's a superior lens.

After four years with my G9, I'm ready to jump to an SLR.

With all the camera systems that have come out in the past couple of years and with those that will still come up over the next few years, I don't think it is a good idea to invest in an SLR at all. If you want to upgrade now, take a breath, erase from your mind the idea that an SLR is the best upgrade option and start questioning if it should be an option at all. Look around at what is happening in the industry and think of whether you will be happy with your choice over the next couple of years.

I think that trying out a relatively inexpensive DSLR for a couple of years is as good a choice as any other right now. These are no longer "forever" decisions, and you should have something that you enjoy and are using to take pictures now, not after a couple years of waiting. As far as the starter lens, I second the notion of the Canon kit 18-50mm lens. It now has IS, it's not too large and after some time with it you would have a sense of what other lens capabilities you would like to add.

Thanks to all for many good thoughts. As always, the members of this forum are numero uno as far as good advice goes.

As some background/context (which might have been informative to provide initially), my "passionate" avocation is as a medium/large format b&w photographer and author (articles written for "View Camera" etc.) but I also really enjoy digital. I know from both digital and my b&w film work that my most used focal length is moderate wide angle, though I do use moderate tele for some digital images. Generally the G9 meets those needs, but I'd like 24 equiv at the short end (vs. the 28-29 equiv on the G9). I wouldn't mind a longer tele but that's not really critical. So the 15-85 lens seems like a good suggestion, especially given its quality (though it's not cheap).

I've held off a long time on an SLR (partly waiting for refinement of "live view", which has evolved over time). As I mentioned, I was ready to go for a T2i until I saw that the T4i is pending, so am waiting. The fact that things are constantly improving doesn't scare me: If something works for me I tend to stick with it if it continues to meet my needs. I'm just waiting to see if the T4i is a significant revision to the T2i/T3i.

Sorry to go on at length; again, I REALLY appreciate all the comments; they are helpful and informative. If anything I've mentioned prompts additional thoughts or advice, I welcome it!
Paul