In that case, use whatever you prefer. The fact that you are even considering the morality of using OSS over proprietary means you actually want to steer away from the latter given the choice. The only questions remaining are: Will the OSS alternative allow you to do your work as efficiently and effectively as the proprietary one at the minimum? Will using the OSS alternative negatively affect others using proprietary software that you need to work with?

The problem is that your tools are going to have to be compatible with other people's tools.