A 3/4 is essentially a big topper. You still have to worry about color and blending and such. A full cap has none of those issues but can be arguably less realistic in the temple/nape areas.

My hair is totally shot so anything is better than what I started with. I went from a topper to a full cap and never looked back. Guys like Dino have gradually increased their base size over the years with great results.

Try a 3/4 and if that doesn't work break out the clippers and go all out. One thing I have learned though is that you probably won't regret replacing any hair that is in bad shape.