Either way is only as good as the tightness of the fit. Most really period correct were just hot fitted no solder or glue. The mechanics of the fit are most important to the strength of the joint.
Solder done right is nice, but difficult for the most average hobbiest to master - can look real ugly. You need to know your solders and be able to do it without destroying the blade's heat treatment, leaving any residual flux (acid), and get a complete seal. Then there is the clean-up .... like I mentioned can get right ugly.
JB weld will do the same job and if done correctly be invisible. The main purpose of either is to seal the joint from contamination and corrosion not strengthen the fit.
There are plenty of tutorials for both on Bladeforums.com and KNF.com if you do a search. Just choose the one that fits your skills and be prepared to practice a bit if you want to get good results.
Carl covered it and there are plenty of videos out there to help you. I really like the tutorial that Jim Coffee created on fitting guards on hidden tangs. His focus was on stainless guards, so it will be easier with brass. I mill or file my slots as close as possible to where the slot is just under sized for the knife tang, force fit it on with a piece of rectangle tubing and hammer. You will need to remove the guard and sand the face of any distortions of the material after driving it into place. after that, I fit the guard back into place with a very small amount of JB Weld to prevent any moisture from getting to the tang in the future.