It really depends on the nature of the suggestion.
If it's a bug, it should definitely be put on the tracker. Otherwise, it probably should not go in the tracker right away. Python developers have specifically asked that the tracker not be used to create discussions, but to track implementation-specific aspects.
You can also post to Python-dev, though you should also be careful there also. Python is a complex project. Because it's more of a platform than a project, it has vastly more restrictions on it than a typical open-source application. Therefore, developers will be resistant to any change which isn't an immediate and obvious benefit. In general, I would advise against posting to Python-dev unless you've had at least some time to read through some of the interactions there to get a feel for the types of suggestions and discussions that go on there.
Generally, I think the python-dev list would recommend you post first to comp.lang.python and start a discussion. Rally some support from a vetted Python maintainer and others in the community. Be sure to show that you have considered the negative implications of any change you are considering and how you would mitigate them. A lot of times, it's good at this stage to have a reference implementation (maybe even something on the package index) that others can install--if it is indeed useful, people will use it and the need will be more apparent. After you've gathered some support from the community, you can then move it (possibly) to python-dev to get more feedback from the core developers before submitting a PEP (Python Enhancement Proposal).
Good luck!