Is Munich the base malt for the beer? If it is, Munich light is easier to work with, enzymatically. Munich dark is tougher to convert and usually isn't used as a base malt. It is not a bad idea to start out in brewing with learning what the different types of malt are used for.
If you are able to find and want to use a malt that would be prime for Leffe, try Dingemanns Mouterij. I have used a couple of sacks of the malt for Lager and always thought that if I would brew a Belgian style, clean, Ale, I would choose Mouterij. The flavor profile from the malt, produced from a tri-decoction mash, leans more toward Ale, than Lager. It converts easily, using the English brewing method. The flavor is very close to Munich. I prefer Mouterij because it isn't as agressive as Munich. To each his own.