I have been thinking which to use.

I am already using Google App Engine (Java) for a few years, running a couple of web apps on production. And paying them ever since they started charging.

I tried a few apps on Dotcloud, but never yet deployed any on production.

Here’s what I think of them.

GAE

+ Reliable
+ Great Docs
+ Great Community
+ On demand scaling

- Some restrictions
- User Agent has GAE..

Dotcloud

+ Shell access
+ Can use pip install
+ Can run worker processes

- Too much things to handle
- Easily use up workers/services - Redis, MySQL, Python, ...
- Higher startup cost

Conclusion

As a one-man-show developer, my bet is on GAE.

Though it is less flexible, it will save time and money.