I'll just vote against the trailer to offer an alternative viewpoint:

This only applies if the the trailer is going to get used at least several times a week.

A trailer effectively doubles your rolling resistance in terms of there is more rubber on the road. I constantly hear people tell me that they don't know it's there unless they hit a hill. I certainly can.

You need to decide ahead of time if you want to use the trailer or not. Depending on your routine, this might not be a big deal. Really bugs me.

When the bike is locked up, you need to figure out how to lock the trailer too. This has become a sufficient hassle that I just don't bother locking the trailer anymore.

Braking at speed is tricky. The trailer tends to 'push' the bike around. This can be compensated with a change in technique, but then you still need to think about the trailer before you grab the levers. I can tell you that on the occasions when I've panic stopped with the trailer, I've regularly gone over, and I've always come close. It's just my gut reaction to grab a bunch of front brake. The rear end gets pushed by the trailer, and if I don't react quick enough... This only happens in panic stops, mind you and those don't happen that often.

If the kids are in the trailer and the raincover is on, I can't hear what they are saying to the point of comprehension unless I stop the bike.

That said, they do offer great weather protection for the kids / cargo. You don't have to haul with you when you know you don't need it. And if the bike goes over, the trailer stays upright.

Like all things in life, it's all a tradeoff. In my particular case, I'm fixin' to ditch the trailer in favor of a dedicated cargo / kid haulin' bike. Then again, it won't be my only bike so I don't have to take it unless I want / need to.

What's the weight difference between the two bikes?