For a scrapper WM/SD is one of the best combos out there. You can soft-cap, buff HP, and get a huge damage buff from AAO. I posted a build elsewhere in this forum. Shield Charge is also a fantastic AOE to layer on top of WM's AOEs.
Can't really talk about other secondaries much -- You could build a sturdy WM/INV and a WM/WP. But on a scrapper, I really favor +dmg secondaries like /SD (or I suppose FA if you really wanted to go +dmg).
So I finally came up w/a theme I thought would be fun to pursue for re-building my WM tank and I choose WM/Energy. Got to going along and yes its very early, but had some good/bad thoughts come into my mind and wanted to make sure I kind of got the gist of what I'm looking for in my secondary. I went w/energy because I havent played it yet and thought the theme was pretty good, and because I have a kat/wp that I really enjoy, but didnt want the two to overlap since I'm much more familiar w/that set and its plus'/minus'.
So basically what Im kind of asking is, whats the good/bad of energy? Whats it major draw more or less? Is it a potentially better choice then say Inv or electric? I've got reg/SR scrappers running as well and I dont really want to duplicate them atm so that I can get some legs under my new project w/out thinkin' "oh, I really like xxx/SR better."
Is there a better secondary for WM I should possibly consider? My tank was WM/SD and ya... he just never became what I was hoping for. Though his life was VERY early in my whole CoH/tank build life.