out of your selection iv'e heard good things about the 55 - 250mm IS lens for the price
the thing is about zoom lenses is you tend to use them at the longer end most of the time if you want a walk about lens i would be tempted by the 18 - 135mm rather than the 18 - 200mm but if a zoom lens is what you want it would be the 55 - 250 IS
the 100 - 300mm USM is an old lens isn't it ?? or have they brought a new version of it out
if it's the one i'm thinking of it wasn't that great a better option if it is the old lens and would have to be got second hand would be the canon EF 70 210 F4 i think those lenses can be a bargain
heres an example of one being sold on ebay
http://www.ebay.co.uk/itm/Canon-70mm...#ht_500wt_1361