Any of the three cameras you listed would be a good choice.
They are all the same size, except the S410 is 0.3 inches thicker. And the S410 weighs a bit more.
Looking at photos of the same subject, taken by the SD300 and the S410. The S410 has a slight edge with better detail.
I can't comment on SD400 photos, since I have not seen any yet.
If movie clips are important to you, either of the SD cameras would be better.
Here is a look at the specifications side-by-side:
http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=canon_sd300%2Ccanon_sd400%2Ccanon_s410&show=all
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I am looking for a new ultra compact camera. Currently have the Canon S30 and looking for something new. I don't use it for any professional-like use. I use it for vacations, parties, etc. This includes bright sun, inside, flash use and night. One other important thing to me is action shots. I use it a lot on the golf course. I have been looking at the SD300, S410 and SD400. I don't print that often and when I do it is almost never larger than 5x7. Majority 4x6 and internet. What can you guru's offer! Thanks all, JS

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