The most pleasant is the one you're most familiar with. I still use gas with at&t syntax.

MASM's niceties go far beyond just syntax, though

	▲	tengwar2 a minute ago \| parent [-]
		I last used MASM back in about 1989 (with MS C on OS/2 1.0). Do you have any hints on how it has changed since then? What is nice about it, and why does the debugger not match up to CodeView?