I have walked both of these routes and think that in April I would go for the Vdlp/Sanabrés. For me the perfect time to be on the Norte is when it is early summer (say, June) so that the weather is likely to be warmer and drier (no guarantees of course) and all of the many tourist accommodations are looking for pilgrims to fill their rooms before the onslaught of real tourists in late July and August.
April/May is IMO the perfect time for the Vdlp/Sanabrés, which is bursting with color and life in the springtime with carpets and carpets of wildflowers, lots of babbling brooks, emerald green fields everywhere and moderate temperatures. The Vdlp rarely gets any of the crowds that the Norte, Frances and Primitivo do, but in spring you are likely to have a nice manageable pilgrim bunch to accompany you. The Vdlp cities are, again IMO, the best list of any Camino -- Sevilla, Mérida, Cáceres, Salamanca, Zamora and Ourense are all amazing (not to say anything bad about the the Norte, with Bilbao, San Sebastian, Santander, etc.).
Levante is another great springtime choice, but you probably wouldn't have time to get to Santiago unless you are a superwalker. And Kinky's suggestion of Madrid/bit of Francés/Invierno is also a great one.
But Nomadboomer, if you have the bug, this will not be the last one, so there's no need to agonize too much -- whichever ones you don't walk this year will be on the list for next year! Buen camino, Laurie