Of the ones you listed the Canon A70 is the best camera. Focus assist light and sound for memos and movies are just some of the features missing from the 3100. The A70 is a camera you can grow into a little more if you are interested in improving your skills.
But for the same price – just under $300 online – you can get a Minolta 414. All of the reviewers are saying it is an incredible deal right now.
http://www.steves-digicams.com/2003_.../s414_pg5.html 4X optical zoom and 4Mp alone put it in the $400 category. It has an all metal body, excellent lens and more features than any of the cameras you listed. You might not ever need a 15 second exposure with noise reduction, but it is a great thing to have if you ever get interested in night shots. And if you are trying to nail a rugrat the continuous focus that focuses right up to shutter release rather than fix the focus as the release passes the halfway point will eliminate a lot of frustrations. You won’t understand what a great feature it is until you get something without it and find that your subject is blurred because they moved during the shutter delay. I have a 5Mp Oly that doesn’t have the continuous focus and absolutely hate taking images of anything in motion compared to using my other camera that has it. None of the cameras you listed have continuous focus.
Another feature I like on the Minolta is the B&W LCD on top of the camera. If your only way to get information is through the LCD you use more battery and can’t read it in bright sunlight. The cameras you listed are missing that. I had always taken it for granted, but my little camera without one is a constant irritation to me.
All of the cameras you listed and the 414 use CF cards and AA batteries. None come with a charger, so you will have to invest in a charger and at least one set of NiMH batteries. They also come with too small a card for normal use – as do all digitals. The good news is that CF cards are very reasonable lately. Get a good brand – they don’t cost much more.
It is a mistake IMO to select the Mp size based current use. Those photos are your memories and you want them in as high a quality as possible. You can’t anticipate future needs or whether you might get that great shot you want blown up to put on the wall. The 414 is bigger than the A70 but you get a larger color LCD and the very handy small LCD on top – not to mention more zoom and pixels plus better features. If the size makes a big difference to you go with the A70.
http://www.nextag.com/Minolta_DIMAGE...414zmainz2-htm