Hi Raquel , Nice to meet you ,welcome to the forum , i'm sure that you will enjoy it , it is the best
Choosing a topic is a very difficult process as you need to read more and more , everyday you will find a new thing
I'm Huda , from Egypt , i prepare M.A. in methodology and really i passed through the stage which you are in and i know that it is very difficult ; try first to choose one of these two topics and concentrate on it , may be i prefer the second one as both vocabulay and games are very rich areas in which you can find many things , you can mingle 2 or 3 games for the same word , it is also encourage co-operative learning in the classroom and has many positive effects , i can help you in that as one of my colleges write his thesis on vocabulary and really it was very good .
All the best