Neither bikes look like they take fenders so for rain it won't be ideal. I have a Langster, and a dedicated commute bike. The Langster never sees the rain except by accident.
The Langster will undoubtedly be lighter if that matters to you. The downtube on the Langster is also pretty stiff so power transfer on the Langster should be better too. I have ridden a few steel frame bikes, and my Langster feels stiffer out of the saddle than a Sputnik, IRO, and Surley.
BB stiffness may not be your primary concern... but I do a lot of miles on my Langster and some of it is in a race-type setting (individual timed Time Trials for example)... so it matters to me that its lighter, stiffer, and handles like a road race bike....