I prefer the FX-888 slightly over the WES51 (give or take the "D" in either model). But that's just me. It probably comes down more to tips and solder; as long as the tip is hot, it's more or less what you do with it that matters.
I've also used a few of those hot-shit thin instrumented irons, there's an upscale Weller out there that's not too bad, or if you want to go all Bentley on it, the Metcals, and I don't know how many others. Thin tip, light handle, very fast (heats up in seconds), very powerful. The cheaper of these sorts aren't too bad I think, but the price goes up steeply from there! If you're doing professional assembly all day every day, by all means get one.
Tim