I am going to pull 240v to my garage to power a welder and other shop tools. I am wondering what wire to use. It will run probably 100' to my garage threw 3/4" conduit, then I'm thinking a new panel. I currently have a 40 amp lighting panel.
The other option I was considering was just pulling another line to power a 240v 50 amp subpanel. Please give any opinions.

You cannot have more than one feed to a structure.

If it were me I'd upgrade the current panel to a 70-100A feeder and pull the welder circuit from there.

I kind of thought that was the case. I think that's what I will do. Plus it will allow for extra space to add more receptacles and lighting in the garage, especially since I was thinking about remodeling an attached room to my garage.

Thanks for the help.