Not much info to go on here, maybe you could clue us in? What kind of valves? New, old, REALLY old? What kind of supply tubes?
Chromed copper? Brass? Flexible? What kind of connections at valve and tub faucet? Metal tubing usually utilizes a "rubber" slip joint
seal and brass friction ring under the nut. If the rubber is really soft, the nuts sometimes need retightening a few times. If the rubber
came from China, anything goes! Did you actually tighten up the nuts as the plumber said? Did it stop the leaks? Did you monitor it for
Metal supply tubes are almost always "bent" to some degree.
Is the leak stopped? If so, why are you considering replacing this and that? Is the "plumber" a REAL plumber?