Originally posted by Bob from Aus Two question to ask yourself is
1. if you are a reluctant lens changer particularly outdoors where telephotos are used.
2. do you have specific things you want to photograph
If you are reluctant to change lenses and your photography subjects could be anything that meets your fancy at the time, you would probably get better use out of a high quality zoom.
I have not used the 60-260 but I believe it telescopes out to be longer as you zoom. This might be a factor for buying the 300mm which does not change length making it more robust, easier to balance and requires less staying power when holding the lens up for significant periods.
I have both lenses and agree with points 1 and 2. If you're looking for a great general purpose outdoor lens, the DA*60-250 is hard to beat. If you don't mind changing lenses, have multiple bodies and/or want to photograph something specific that requires more reach, the DA*300 might be the better choice.
Regarding the issue of the fact that the 60-250 extends when you zoom to the long end, that is true, the lens does extend. However, it only extends by 2 inches (5 cm) from its shortest length to its longest length and the balance point of the lens doesn't change dramatically as a result. So in terms of handling, I would say it's a non-issue. Don't get me wrong, I would prefer that it was an internal zooming lens (even if that meant it was a little larger), but it's not really a major issue in practice (IMO).