You will never go wrong getting the heavier jack. If choosing between the 3000# and 3500#, go for the 3500#. One thing you need to remember, not only does the jack lift the camper, it also lifts the rear of the tow vehicle. Get the heaviest one you can find. You never know what's ahead in your future. You may someday get a new tow vehicle. For $50 difference in the tongue jacks, it's well worth it!
Also, get the 24 inch. That ONE time you camp on a hill, or a dip, you'll be glad for the extra length.
I had an electric jack installed on my Outback. It has a foot that has notches so the post can be lengthened. With the height of the truck receiver hitch, I'm GLAD I choose the longer jack and still use the extension on the foot.