A reader emailed me this question:
First of all, I really enjoyed your Travel and Photo Journalism presentation on Saturday, thank you for some great information. Also the Flash Presentation was very informative.
I use a Canon XSI with a Sigma 18-200mm as a walk-about lens. The lens has a good lens hood, however I also have a circular polarizing UV filter on the lens and , with the lens hood on, I have difficulty adjusting the filter. I typically don’t use a tripod so I run out of hands and fingers at the wrong time! Because of this complication I don’t use the Hood most of the time, any suggestions as to the benefits of the hood vs. the filter if I can only use one.
Good question, and one that may be useful for others too.
I still advise using both… I have a 70-200 and with the hood it’s quite tricky to adjust the polarizer: but I still do it quite often.
So I would say:
- Lens hood: always. For stray light as well as for damage protection.
- Polarizer when you need it (when the skies are blue, etc, or you want to reduce reflections, or you need to cut light).
- Both when you can, and especially when you are shooting against strong light
I feel the reader’s pain… it’s one of those things where we wish it was different – but it isn’t… 
The other thing to consider about a polarizing filter is that it (depending on quality) reduces the light by about 2 stops.
It might be worth going for the lens hood and using the filter when you can see a need, also as you get closer to night you may want to consider the camera blur from the filters reduced stops