Roe v. Wade? How about Run v. Bike?

Roe vs. Wade?  Well, since I have no current disputes with anyone named Roe and the
other Roe v. Wade is way too controversial for this site, let's skip this one and move
on to Run vs. Bike.

Which of these acitivities provide the best fitness level? Fewest injuries? Weight loss?
 Best effectiveness for time spent?

Not that I am an expert in these matters, but I am leaning towards a mixture of running
and biking as the most efficient method of fitness. 

For the last several years, I have found that while bicycling alone kept me in shape, it
did not really tax my cardiovascular system to the extent that would make significant
levels of improvement.  In other words, I hit the plateau pretty quickly.  I became so
efficient that one year during RAGBRAI*, I rode 500 miles in a week and gained four
pounds.  Other people get a little more crazy on the bike.  See the movie "Bicycle
Dreams".

I have always found that running increased my fitness level the fastest.  However, hard
running is hard on the body.  Even at my not-so-advanced age, I prefer not to run two
days in a row.  If I run three days in a row, I'm pretty stiff.  Running has its share
of crazy people too.  See the movie "Running on the Sun" or the book "Born to Run".

For the last few months, I've been trying a regimen that mixed running and biking.  I've
tried to get a workout five days a week.  My fitness level has increased and my weight
has slowly been dropping.  It seems that running has provided an increased level of
difficulty in the workouts while cycling has given my feet and legs a break.

Let me know what you think, cycling, running, or both?

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*RAGBRAI - Register's Annual Bike Ride Across Iowa