There’s a ‘Where to start’ FAQ linked in the sidebar wiki for this community. I recommend going there and taking a look.

The best place to start largely depends on your personal preferences in terms of whether shows need to be action packed, have long term serialization vs episodic, and tolerances for 60s or 80s/90s trends in special effects, technobabble, Shakespearean acting styles.

I’m an older person who has been watching since TOS was in first run, and saw the original Star Wars as a teen. Alien 1 too. All to say, I saw all of it as it came out. We were just so glad in the late 70s that someone was making sci-fi movies that weren’t post-Armageddon dreary.

Trek has held my interest more intently, but I read more than my share of the SW ‘legends’ books as they came out. I can see a wide range of offerings in both franchises, appealing to different audiences and tastes.

It rather boggles me that there are folks who have tried one but not the other. It’s like someone who is a DC or Marvel fan and has never checked out the other. You may not find anything to like, but the potential of finding another universe of stories that interest you is more than worth the risk.

A word of caution. Just about Star Trek every fan thinks that the show they first watched or their favourite show is the best place to start. They’ll argue passionately that you’ll do best starting where they did. Ignore all of it. You’re you.

Read the ‘where to start?’, check out ‘Memory Alpha’ or Wikipedia for the basic description of the main series, pick one that appeals and try the pilot. Be also cautioned that many of the shows take a while to find their groove. Checking out a ‘best of’ list for early seasons is ok if you’re not the of a completist temperament. Hope you find the Trek that’s best for you.