I first commuted from St Pancras to SE1 with a hardtail mtb on slicks and for me that bike was perfect for thick traffic which I like to think of as singletrack with moving obstacles. I had a hoot on it. I switched to a road bike and hated it - nervous handling, relatively weak brakes and a prone position. MTB was about 5 mins faster.
I first commuted from St Pancras to SE1 with a hardtail mtb on slicks and for me that bike was perfect for thick traffic which I like to think of as singletrack with moving obstacles. I had a hoot on it. I switched to a road bike and hated it - nervous handling, relatively weak brakes and a prone position. MTB was about 5 mins faster.