I was this discussing the question of correct word placement in english with a coworker but since we both aren't native speakers we did not come to a conclusion.

Here is an example: Given the sentence

We have no open positions available.

which of the following placements of the word currently are valid?

Is there a simple rule which explains this?

1. Currently we have no open positions available.
2. We currently have no open positions available.
3. We have currently no open positions available.
4. We have no open positions currently available.
5. We have no open positions available, currently.