Can anyone tell me..

More like a reboot a la Casino Royale/Batman Begins. A reboot that eventually became a parallel timeline to the original trilogy that got synched up with it in Days of Future Past, becoming one timeline again.

I like First Class the most, but as for where to start if you've never seen any of the movies before, I'd say go with the first X-Men movie, watching them in order of release date, skipping Wolverine: Origins.

X-Men
X2
X-Men: The Last Stand
X-Men Origina: Wolverine
X-Men: First Class
X-Men: Days of Future Past
Deadpool
X-Men: Apocalypse

I would actually go in the order of the actual timeline of events which would mean:

1. X-Men: First Class
2. X-Men Origins: Wolverine
3. X-Men
4. X2: X-Men United
5. X-Men: The Last Stand
6. The Wolverine
7. X-Men: Days of Future Past
8. X-Men: Apocalypse

Most people will probably disagree with Days of Future Past going 7th instead of 2nd but it doesn't technically take place right after First Class like many people would think because it is an alternate timeline that only happens with the future X-Men going back in time between the events of First Class and Origins so really it should only be watched after. The reason being that none of the events in it have happened yet for X-Men 1, 2 or 3 so it would be inaccurate to see it first

That's how I would do it anyways - I think it is interesting to see how Professor X, Magneto and Mystique all came to know each other before watching the original X-Men trilogy. Then it gets all reset with Days of Future Past so then you watch Apocalypse to start following the new timeline...