High-level languages are hard to obfuscate. If you're going for difficulty in decompilation, you're pretty much stuck to low-level, non-interpreted languages.

.NET and Java are your best bets for relatively high-level desktop languages that are hard to decompile because since they're so widely used, obfuscation techniques are more advanced. But really if you want to create a difficult-to-decompile program, I think you're pretty much stuck with C or other non-interpreted, low-level languages (maybe try D?).