I'm torn on which of my bikes to use for winter commuting. I ride about marathon's distance each day.

The first option is the purpose-built commuter. This would be the natural candidate because it is pretty much zero maintenance with internal gears and a belt drive, plus the roller brakes work equally well wet or dry.

But the roller brakes just don't work that well in general, and when it's dry a set of v-brakes easily outperform them. Plus, it's a really heavy bike and adds about 5 minutes to the commute. And you can't take it on the train during rush hour if the weather really sucks. The range on the Nexus hub leaves something to be desired for the hills. Lastly, it's a PITA to remove the rear wheel to replace a tube or swap on a studded tire.

The other alternative is my folding bike, which is considerably lighter and whose rim brakes are very effective on the smaller wheels. Of course it is welcome on the train. And it has twice as many gears (16 vs 8), so hills are easier. Of course there are cogs and rims and a chain to keep clean, so that's a pain. but I'm seriously thinking of getting a pair of studded tires for it and going that direction.

Thoughts?

That's a pickle, alright. The Soho (I assume that's what it is by your description) sounds ideal for riding in the slop, but not so great for your particular commute. The folder, OTOH, sounds great for your commute but not so good for the slop. Having ridden both a traditional drivetrain bike and my own IGH/belt-drive setup (I own a 2010 Norco Ceres) I understand what a PITA it is to keep a derailleur drivetrain clean and working in the winter. That being said, for me the most important factor of my commute is that I enjoy it. It sounds to me like the folder would make a much more enjoyable ride for your commute, and that enjoyment would overshadow the hassle of keeping its drivetrain clean. Just add the studs, some Kool-Stop Salmon pads, and make sure you're stocked up on cleaning supplies and chain oil.

Great advice, thanks. I have the koolstop pads and was on the border of getting 20" studs. Maybe I'll just go ahead and do it...

I don't have any IGH experience, but I would test it out in cold weather before committing to using that as your winter bike. Grease and other lubricants are a lot thicker when it's cold out, so I'd be concerned that the more complex mechanisms in an IGH may not work as expected in some weather conditions.

IGH are great for the winter and actually seem to be preferred by many winter riders. I don't have one but have already dealt with the RD freezing up from road slop on several rides despite the full fenders I run. Before next winter I will have an IGH setup to use. Oh and wheel rim brakes can freeze up also, not a lot of fun when you need to stop now.

Use either one when the conditions warrant it. Irclean has definitely got me thinking about adding a bike with an IGH and is belt driven (I am still waiting for you to send me the bike so I may verify your claim that it is a "dream to ride" ;-), but in the meantime I will use what I have.

When I know the weather is going to be nasty or I have some shopping I take my bike with fenders and rack. If I'm not going that far and the roads are clean I take my bike without them.

I have found Sturmey Archer drum brakes , reliable for 20 years, trouble free.

they have IGH/drum brake combinations, and a hub dynamo /drum brake combination .. now.

In My case, they're on my old MTB, freewheel/drum brake on the back ,
front of set also .. UK made, was Elite model named then.
it wears the Studded tires , so for freeze-ups, Black ice, I grab that bike.

I'll send my Ceres to you anytime... all I require is a security deposit of a new, 2011 Norco Ceres.

Is that all ;-)?

Well the igh and beltd rive have been sensational in the winter with no maintenance and no problems. I had not thought of a derailleur freezing when cold, but that would suck. In fact, as i think about maybe i should just slap a studded tire on the back of my Soho (it already has one on the front) and call it my winter bike. It's not as if I'm particularly fast on snowy/icy days anyway...

Yup, a frozen derailleur sucks. I learned to park my bike in 4th gear on the middle ring after the first time that happened. I like having a worry-free drivetrain... and not having to clean my IGH/belt drive setup after almost every winter commute is, to quote MasterCard, priceless.

I'd go with the folder. Having gears in winter is a big help and frozen derailleurs can be fixed quickly with WD40. Just carry the large size in your pannier

So the derailleur has frozen on you? Yikes!

Check weather, choose bike, ride.

Yes; last winter. Unfortunately it froze in 1st gear so it took me forever to ride home. Once I thawed it I lubed all of the pivoting points and then sprayed the whole works with a silicon spray. It helped, but the derailleur still froze a couple more times, hence my decision to leave it in 4th while parked. That experience was part of the reason I bought my IGH/belt drive bike... I wanted a 4-season, low maintenance commuter. Since I mostly stay on the middle ring anyway having only 8 gears was fine with me, and the Alfine is a nice hub.

I still have a couple of derailleur bikes, but I park them for the winter.

oh, so it froze while parked outside all day? I park inside, so maybe that's not an issue for me. (still looking for reasons to go with the folder)

I have had a derailleur freeze on me during a ride - or possibly it just got so clogged with ice it wouldn't work - either way, I could pedal but not shift. I switched to a single speed after that.

But you are wondering whether to go with the folder - I go with a folder, but I have a Montague. I have a single speed, so the derailleur freezing is no longer a problem for me, but if you have serious hills to go up (I usually don't), you might not want to go that way. They make other bikes as well, but none of them has an IGH, so you'd still have the derailleur to contend with, even though you'd be able to take it folded on public transportation during rush hour. I think they're coming out with a full-size 8 speed IGH folder for 2011. Might be worth looking into, if you've got a budget for a new bike.