더 좋다능 seems to be one of the slangy contractions used on the internet.
Compare these, for example:
1. 난 옛날 영화가 더 좋다는 거야 [or 말이야] = I'm saying I like the old movies better (normal phrase).
2. 난 옛날 영화가 더 좋다는 거 [것, 말] = contracted form when space is limited (as in note taking, news headlines, tweeting), or sometimes to make it sound pithy or imperative.
3. 난 옛날 영화가 더 좋다는 = a recent trend on the internet of contracting it even further (ungrammatical).
4. 난 옛날 영화가 더 좋다능 = a slangy version of 좋다는 found on the internet.
#1 is correct and proper, while #2 is occasionally used in certain special contexts. #3 and #4 are nonstandard, slangy expressions found mostly on the internet. People might give you a bewildered look on encountering such sentences. They are unfinished forms from a grammar standpoint.