I want to put up a big clock in my livingroom.

Centered on the wall and push the sofa over a little. Not much difference in the photo.

Furniture and its placement can change but the wall will probably never move, I would opt for the center of the wall and then arrange the furniture accordingly.

I would center it on the wall, so if you rearrange furniture it will still look fine

I would Center it on the wall and make a gallery wall of photos around it.

I would cut out pieces of paper the same size as your clock and pictures and arrange them on the wall to experiment with placement. That way you don't have to commit until you make the decision and hang them permanently. You have a great start!!

I am a gal who is all about symmetry, but if the sofa is not centered on the wall then you should not try to center the clock to the sofa or the wall. Get all your frames together and make paper cutouts. Work on making the arrangement more free flowing by tacking your paper arrangement to the wall. Try to include some other artistic medium like a large initial or a sign. Like things work best in odd numbers. For instance the clock, the initial or character symbol, and maybe a vertical welcome sign. Each piece would have the visual interest of size, and shape, as well as visual weight. Once you have those pieces anchored you can fill in the area with the frames. Unless all of your frames are the same avoid hanging in straight lines within your gallery layout.

I would style this by lying it all on the floor first. Playing with different styles to discover what looks best. Check out studio 12 stencils - they have some neat clock stencils and you could make something really neat for this space and you might be able to make something that blends the photos and clock together. Make it unique...

I'd center over the couch. Here's a post I did on creating a gallery wall :

https://www.burlapandblue.com/2015/04/20/how-to-create-a-gallery-wall/