Location: San Jose
I'm not sure what you mean by 17". 17" doesn't really mean anything, is it at 72 pixels/inch, 100, 150, 300... you get the idea. Normally, you would choose the image size by pixels.. ex: 1024x768
Here's a link to Photobucket's help page.
It looks like there are 2 types of accounts, pro and free. Which type are you using? If free, you would choose the size that you want and they will resize them for you. Most sites allow you to upload your original images and then they will create smaller sizes for you to link to.
On your camera, I would always choose the largest file size. This will allow you to make the best enlargement from the image.
For posting on this site, 800x600 is probably good enough but I always enjoy larger images myself. Just choose the size you want when uploading and you should be fine.
Hope I've been of some help.(I'm not familiar with Photobucket as I use pbase and zenfolio)
I just looked up the specs on your camera:
Number of Recorded Pixels 10MP (3648 x 2,736)
5MP (2,560 x 1,920)
3MP (2,048 x 1,536)
2MP (1,600 x 1,200)
1MP (1,280 x 960)
VGA (640 x 480)
16:9 (1,920 x 1,080)
So the 10mp(3648 x 2736) is your largest file size. I have a Fujifilm f550 that actually gives me a really lousy image at full size so I have it set for the next size smaller and the images are pretty nice with that setting. You'll have to test to see which setting gives you the best image on yours if you care about image quality.