EF 70-300mm DO IS USM or EF 100-400mm F/4 L IS USM

I'm new to the site so I'm sorry if there has already been comparisons. I want to pick up some new glass but having trouble deciding. A one of the main factors is size. I'm stationed on a DDG forward deployed so space is a luxury. The DO would be the obvious choice however I've read some reviews that lead me more over to the L lens. Some say the DO shoots soft and others say the focus is wretched and stiff. Ideally I would choose the L but shooting with a tripod on a moving ship is not plausible. Any insight would be appreciated.

--
[IMG]http://i46.tinypic.com/vew4m.jpg[/IMG]