I haven’t got a huge amount of experience with different canvases because I was very happy with the first type of canvas that I ever purchased. That canvas was Mono Royal Deluxe by Zweigart. It’s quite expensive but it’s good quality with a heavy weight and most importantly it’s always straight when it’s new. It also irons really well and is easy to block if it does go out of shape.
I prefer to us a white canvas because it gives a more contemporary look to the finished work. As you are going to spend many hours stitching your wall hanging it would be disappointing to have it ruined by a shapeless floppy canvas. All my patterns are designed to be stitched onto 18 count or 18 holes per inch canvas. This gives the best thread coverage although the needle will sometimes need a slight tug to get it through the holes.
Mono (single thread) canvases are woven from single horizontal and vertical cotton threads.
There are two different types.
Royal (above) has threads that are not attached at the points that they cross. This means that the size of the holes isn’t fixed so where two threads need to go through the same hole the needle naturally pushes the weave apart to create a bit more room without distorting the whole canvas.
Interlock is woven from threads that twist around each other at the points they cross so that they are fixed. This is a much cheaper canvas that I’ve only bought once. I was very disappointed that it was so uneven when I bought it and no amount of ironing or pulling would get the weave to straighten even after blocking. I don't recommend this type of canvas for stitching my patterns.