A common figure-8 is an 75% strength knot that is bulkier and more difficult to untie. It is, however, the gold-standard for mountaineers, and they stake their lives on its security and dependability. Even after a good hard fall it is not too difficult to untie, though saltwater and time do seem to make this more difficult.
Figure-8, Yosemite finish
This has become my favorite mountaineering tie-in, and I have tested it through more than a few falls, as well as failure-testing it against both splices and standard figure-8s. It is less than line strength, but not by very much.
But what about chafe? A thimble won't work, but there is another solution, well proven on industrial lifting slings and used on my boat for 15 years: cover the wear area - the thimble location - with nylon or polyester tubular webbing. 1inch webbing for line up to 1/2-inch (12 mm) and 2-inch webbing for larger line; a 3-6-inch length will do. The webbing will move with the sharp spots and rope will only feel nylon sliding on nylon, it will protecting this critical area from sun, and eliminate all wear. I believe it out-performs a thimble in many applications and is certainly a safer choice for the beginning splicer, where the thimble many not be as securely positioned as needed and can shift. I have used tubular webbing "thimbles" on mooring lines and high-tec halyards, and the knot or thimble has never been the failure point.