Camera Lens Purchase Help Please

[turd]

I am in need of a general purpose non prime lens for mostly outdoor shots while doing extended hiking/camping, mostly nature but basically all purpose.
This will be on a Cannon EOS 20D, I am looking at:

Cannon EF 28-135mm F3.5-5.6 IS USM SLR Lens

Tamron AF 18-200mm f/3.5-6.3 XR Di-II LD ASPHERICAL (IF) MACRO

Sigma 18-200mm f/3.5-6.3 DC

They are all basically around $400-$500. I know the Cannon IS is very fine but the range is not wide enough, I think?, when you factor in the CMOS.
I also have checked all the reviews and see what others have said but I am wondering if anyone has experience with any of these and what do you think. I really need to know about the sigma and Tamron because they are fairly new.

Thanks

[skotti]

Canon would be my choice and find a second 90-300 lens.
My reasoning is that you want F-stops. The F number is the size of aperture that lens can manage.

Photo 101
low f-stops (2.8-5.6) have little depth of view but allows short exposure time.
high f-stops (16-22) have complete depth of view but need longer exposure time.

Landscapes are taken with high stops and tripods. but if you don't want to hike a tripod with you(most don't). Dropping a f-stop or two can make a sunny landscape hand-holdable.
animals are taken with zoom(until it is tame and that's no fun). When you are have you lens at 200mm your exposure needs to be 1/200 or greater(1/250 on most cameras) for a handheld shot. that means a f-stop of 4 or 5.6 in most conditions other than bright sunshine.
Flowers, plants, bugs are taken with shallow depth of view to throw the background out of focus. this needs a f-stop of 2.8 to 5.6 on the lens.

no more class.

the canon len has a lowest f-stop of 3.5 at 28mm and 5.6 at 135mm
the tamron len has a lowest f-stop of 3.5 at 18mm and 6.3 at 200mm
the sigma len has a lowest f-stop of 3.5 at 18mm and 6.3 at 200mm

My hip bag carries a
canon 18-55 f3.5-5.6 $170
canon 55-200 f4.5-5.6 $270
yes carrying 2 lens is more of a pain but the fact of leaving the tripod at base camp makes up for that. I will probarly replace my long lens with the canon 70-300 f4-56 IS when my wallet needs liposuction. $650

Remember to buy filters too. UV for physical protection and polarized for extending exposures times with low f-stops.