I have SW Premium and we are loving it. However, kiddos, wife and I are all interested in the GOTG also especially after seeing some pics. I personally will not buy a GOTG until I see some real gameplay and know if the code is complete or darn near it. The idea of buying pins with unfinished code and then waiting is not for me anymore. It really feels SW will get done soonish and is complete enough now it probably doesn't really matter to us if we have to wait, but I can wait a while for GOTG.
If you like SW and are wiling to sell later at probably a loss then buy it and enjoy it until you're ready to get GOTG. If you really can only buy one NIB and don't want to mess with selling, then I think you need to wait until probably next year to make a good decision between the two. You need to let the games get out to play them, listen to feedback, see where the code is etc. Only once they are both complete can you really make an informed decision, but I totally understand you may not want to wait.
So, if you want one now, buy SW. Want to wait and make a true decision between the two, then you just gotta wait...