I'm from Boston, I'm running Boston, you can guess where I stand on this issue. The only thing I wanted to say is that you cannot discount London's course for being a time trial. It was intentionally set up that way and they are hoping the course will (and does) attract the best runners.
I have never run London, although I do hope to. The reason why I'm sticking up for Boston is that it is a completely different course than the Chicago/Berlin/London completely flat course. After running 16 miles downhill, having to then turn and run up some long inclines and steep hills is very tough. The course makes running the distance even more challenging. Let's also not forget, this is the 110th running.
One important point to mention is that London is also known for dishing out very large appearance fees to the top runners. Boston will give the hotel rooms and the 4 star treatment, but no one is walking home with any extra cash, other than prize money. Some may feel that this makes the race less prestigious because it won't attract the top name talent, but the race directors don't need to because Boston has its history and still attracts a great deal of talent. There may not be 30 guys trying to break the world record, but overall, the mid-front of the field is just as good as that in London's (that is coming into the race ... the times are different due to the courses).
The reason why I find Boston might be more exciting (and please rebut me .. I like discussions), is that there are so many different points of focus in the race. There's the halfway point, where no one in the last who knows how many years has ever led and gone on to win. There's the hills, a make or break point for everyone. Then there's the downhills after Heartbreak Hill. It all makes for many different points of focus.
I honestly feel like in London, there's only one point, the finish. I won't watch the race at the halfway point, I will only care about the end, who won and whether the winner broke the record.
This is nothing against the folks who think London is better, maybe they're right? I haven't run London (yet), I hear it's an EXCELLENT time. But in the end, 110 years worth of history seem hard to beat, to me at least.
Alright, enjoy this fight, I'm going to rest up. Apparently the race is tomorrow!?!?!?