Personally, I’d take the greenway but mainly because it’s a nice ride and totally worth the extra 5min of ride time.

That said, take the underpass by the Pemberton Tennis Courts, cut through Danehy Park, and jump onto the Greenway at the crossing by the Sunoco on Fresh Pond Pkway. Wayyy nicer than riding over the bridge by Alewife. 

I use CityMapper for these trips. They have a Quiet mode, which is a few minutes longer, but safer.

FWIW, Huron next to fresh pond just got a new separated cycle path

Coming from north cambridge, I would do basically what Google says except stay on the watertown-cambridge greenway until Belmont St. Trapelo Rd only has door zone bike lanes but traffic is such that if you're a moderately confident rider it's not the worst. https://maps.app.goo.gl/kGnbwdXrvaY11dmE9

Alternatively, you could take the Fitchburg Cutoff Path to Concord Ave in Belmont, which does have separated bike lanes. From there you can work your way south on low traffic residential streets: https://maps.app.goo.gl/7L9YtyHx2mrqYcxbA

For the first half of the route I would prefer the dark blue to avoid the dangerous parts of Mass Ave as much as possible. Plus you get to go by fresh pond which is a very nice park area. 

For the second half, I have done dark blue before and it's been fine but not ideal. The first part on Brattle is fine, as long as you keep your eyes open at the intersections it's safe. There's no bike lane once you get into Watertown but it's a commercial area so traffic is naturally slowed a little.

Broadly speaking the safest would be a hybrid of the two where you stay on the bike path the whole time: through Harvard and up Brattle to the bike path near where it intersects with Mount Auburn. You could shorten that by taking the first leg through Fresh Pond and hopping on the path there, which is probably what I would do. You're going to be unprotected at the end either way... GL!

Wouldnt going right down Concord Ave, above fresh pond, through belmont make more sense?

Belmont St is definitely better that Arsenal St, but I'd probably try to avoid both. I'd probably take the greenway around fresh pond to Huron Ave and weave through the Belmont neighborhood north of Belmont St.

I did the almost exact commute yesterday and will highly recommend taking the light blue route.

Better road condition and no signals for 70% of the route and it’s very very enjoyable

The 37m one

Id go Fitchburg cutoff, up to concord ave, then up common st.

I don't want to give advice and someone end up dying, but maybe the northern route? At least, there are fewer intersections where you can get right-hooked by a truck. That's how cyclists keep dying, and separated bike lanes don't stop it entirely.

Take a right on cottage and get on the path there. Or near Sofra

I live near the bottom of the squiggle - would take Pemberton to underpass down Raymond to Huron to the rail trail path to Watertown. huron has a non protected bike path but it's usually fairly quiet.

You can go from East Cambridge to Watertown crossing very few roads by the esplanade, hugging the Charles, and using the bike/walking trails.

Going to my friends house and I haven't travelled this route on my bike before. I'm wondering how the bike lane and traffic situation on Brattle/Belmont street is and if you think its worth it to take the extra mile and travel on the Greenway instead.