I am in the process of putting new line on my reels,the rio line i have has two welded loops on,for attaching line loop to backing which knot would you use i was thinking about the improved clinch knot? thank you

I used the perfection loop on my backing and so loop to loop worked for me. If you get into your backing on a regular basis playing larger fish, then I would consider a different knot since the backing loop will tend to cut into your fly line loop.
There are more experienced anglers here that will surely give good suggestions.