#4. Just make sure that the "nice way" to explain your brain's rebellion at the physical contact amounts to lack of chemistry, etc.

#2 is a runner-up, as it's not technically a lie (it's you and him, as you could be boring enough or needy enough to want a milquetoast, but aren't; it's just not something to aspire to).

Either way, you want to go with an option that makes it clear that another date won't be forthcoming. 1 and 3 both offer hope.