'I take a liking to you.' and 'I'm liking you.' are both poor choices of sentences to express affection. The second one is used sometimes by modern native speakers; but it's use is already criticised and it will die out, ie become uncool and fade away. These things are self-evident sometimes. The first isn't correctly constructed at all: it's clumsy and arguably isn't actually a complete sentence, either. 'I like you.' 'I am beginning to like you.' 'I am getting to like you'... (and others) are much better choices because they are correct.

The first one should be ‘I am taking a liking to you’, but I am not sure anyone would say it.