Past because it wouldn't fuck up the timeline as badly. If I went to the future there would be no me in the intermittent years to create descendants. Back to the Future screwed the pooch on that one big time.

On a serious note if I could change the past of say...a parallel world and I had 100% knowledge that I'd be guaranteed to survive and not create a paradox...say that I created a new universe on time travel and could live in that one alongside the consequences of my actions...

I would actually go back in time not to invent a technology and make money, but the thing I'd most want to do is advance human technology by a few hundred years. I'd want to take our knowledge of science back in history so that the development of humanity could be sped along.

Of course since I came from a time where time travel was a thing, I'm not sure how much more they could create but it'd be fascinating to me to see how different the era I came from would be if they got a headstart. I've always been interested in that as a thought experiment. Because scientific growth is exponential and once you get to the computer age it accelerates even faster.