Essentially, both your choices are imperfect. You want to match CPU with GPU to get best performance per dolar spent. So, you would either want 6100+1050 ti as cheaper option or 6400+1060 6Gb as better option. Otherwise you create imbalance where either CPU or GPU will bottleneck.
Another factor to consider is the fact that 1060 3Gb is not that great at all. In some games it performs no better then 1050 ti. You would probably be better served by rx 480 4Gb instead.
So in the end it's all down to the games you play. If you play CPU-heavy games (BF1 for example), 6400+1050 ti combo would be better. For a GPU-heavy games, 6100+rx 480 4Gb would be better. And if you can scrap a little bit extra, 6400+rx 480 4Gb combo should make you happy, at least for now. My crystal ball got broken, so won't tell anything about next 2 years, though

Hope that helps.