Which tense to use when presenting my master thesis?
I think it really depends on what the research shows. If the research demonstrates a process that is ongoing, or straddles multiple timelines/periods, you can go with "the research shows that". However, if it is related to something that happened squarely in the past, you can use the past only. 

I personally tend not to use the first person when discussing results of undertaken research, though I have seen it done in all the ways you describe. Really it comes down to what feels most natural and right to you as the author.