Aquavit or Maialino
Tough call. Depends on your taste. Were you having a regular (non-RW) dinner, I'd say Aquavit for sure (though they're both good) - but given it's the special RW menus, it's really a matter of taste. They'd be staggeringly different meals, and staggeringly different cuisines.
One's an AYCE buffet of pickled & smoked fish, salads, cheese, swedish meatballs, etc. It's not as "cheffy" / refined as their normal (especially dinner) menu options, but it's a lot of fun - and if you like herring & salmon as much as I do, a heckuva deal - being AYCE, it's as good a deal as your stomach capacity is capable of making it. And as one who shops at Russ & Daughters quite frequently, I know full well that (good) herring and lox ain't exactly cheap. Is it really an example of what the kitchen is capable of? No, but it's all top quality, well made, and if you're not prone to eating Scandinavian food as often as we are, something quite different than the norm. Like I said, it's fun.
Maialino, on the other hand, will be a plated three-courser. They actually (unlike a lot of RW joints) have a decent selection as well. Heck, I'd be happy to do both lunches if I had two open afternoons to do them.
So I guess my answer is... I have no answer. For lunch I -personally- might lean toward AQ just a smidge, if only because at lunch I usually don't want anything so heavy as a pasta, that's more dinner-food for me. But that's just personal eating habits. They're both great restaurants.
(I will say like AQ's bread better - their dark, slightly sour rye... so rich it's almost like a cake... pile it up with herring and Västerbotten... mmm...)
Thanks for your thoughtful inputs! Like you, I looooove dark, rye bread. I aksi read that AQ bakes their bread in house, so I'm really looking forward to it. :) Based on your suggestions, I think I'll head to AQ then. A caveat is that I''m vegan, so I won't be part taking in the fishy goodness, but I''m sure my mom will and this is supposed to be a special treat for her. I've been to Maialino before for lunch and I didn't like the bread (very pedestrian) they served, but the uovo pasta? My mom really enjoyed that. The pasta portion at Maialino isn't large, so a food coma isn't my worry :P I've read some diners (from Opentable) were disappointed that it's not a plated three-courser at AQ and that the RW diners were 'stuck' in the back dining room and not the main one. I don't really mind, I mean, if you really want the most 'authentic' experience, you wouldn't go for the AYCE route, would ya?
Ah... had you mentioned your vegan-ness I might have answered differently. Either one might be difficult - I mean, at AQ you'll basically be stuck with... bread and potatoes. You couldn't even slather on the great Nordic butter. There might be a couple salads as well.
You could - to make it more exciting for yourself - add an extra dish from the a la carte menu, I'm sure. There's usually at least one vegetarian app and entree on the lunch menu at AQ, usually very good, well-thought-out ones and not just token salads and such. Probably one of them could be made vegan by leaving off an element - never hurts to ask them.
That said, there isn't a single Secondi on the Maialino menu that's vegan - though I suppose they could up-size one of the antipasti for you and use that as a second course, they're pretty accomodating. Hard to say what would be vegan, though - even there, there are only three options, and one of them is a generic salad. The artichoke mousse may very well have cream or butter in it, so no way to know about that one.
I also find the bread at Maialino less than exciting - but Italian bread in general I find less than exciting, with the exception of focaccias and such.