The lighter the string the softer and quiter the tone, maybe even slightly more tinny sounding BUT easier to play. The heavier the string the warmer and richer the tone, a bit more bassy too BUT maybe HARDER to play.
We recommend you go for the thickest (heaviest) strings you can play in COMFORT, to get the best tone.
Acoustic guitar strings come in 3 main gauges (generally speaking)
Extra Light XL : 10-47
Light L: 12-53 (sometimes 12-54 etc) - as fitted at the factory to 95% of acoustic guitars.
Medium M: 13-56
So 'Medium' strings are just about the HEAVIEST strings generally, so be careful when asking for medium strings.
Electric Strings - some advice on gauges
Extra Light: 8-38 use these when you want the thinnest, easiest to bnd strings
Light 9-42 fitted as standard to MANY guitars like Strats / Tele, Ibanez
Hybrid 9-46 as fitted to Gibson Les Pauls / SG
Regular: 10-46 fitted as standard to PRS and some Fender Custom Shop
When changing strings, if you are new to it then go for the nearest make and gauge to those already fitted. If your guitar has a tremolo then changing make or gauge may require a set up on your guitar. Even if your guitar does not have a trem, your guitar NECK may require some adjustment to cope with the increased / reduced tension. We're here to help and happy to advise so feel free to COME IN and ask.