Both Shimano and SRAM make front mechs that don't rub. If they do, there's a fault and it can be caused any number of problems from bent chainrings to faulty alignment or stiff chain links. Shimano's cheapset FD, the Alivio
, will give buttery-smooth silent front shifts when set up properly, with no rubbing.
If there's wear or deformation on the chainring ramps; that can cause 'rubbing' symptoms as users try and adjust it out in order to regain smooth shifitng. If as you say, you have 'constant adjustment' then you have constant wear.
If any of your drive train is worn, and it will be if the bike gets regular use, then no amount of adjustment will fix that.
Re 'index shifters are more trouble.' If you got wear, you got trouble. The only way you can be sure is to replace the chainrings and front mech. Index shifting is flawless when it is not worn.
If you had a faulty index shifter, then you almost certainly will have resultant wear on the FD plates and chainring ramps.
Replace the FD first, and if you still have problems, replace the chainwheel/crankset, and chain/cassette. If you have the FD rubbing or noise from the FD plates, and you can't calibrate it out with a turn or two of the barrel adjuster on the cable, then you have wear or mis-alignment, or both.
FD mechs, chain rings, chains, guide wheels, tension wheels and rear cassettes are all consumable items.
If you start replacing any of this, check the bottom bracket and cranks for play first. If you just a have slightly bent chainwheel it can be moderately de-bent in a vice with care. Otherwise, new FD and chainwheels, chain and cassette will fix it.