If there was a bad hum on them then the amplifier itself was probably cheap so that means the speakers were cheap, 2-3 watts might even be pushing it. But you at least have a ballpark. It's not always bad to overbuild an amplifier though, as long as you're cautious with the volume control, a higher wattage amplifier using a lower volume setting on lower wattage speakers will generally sound better than an amplifier turned up to 8 or 9 to get the same output power. Just don't turn the higher wattage amp up on lower wattage speakers or you'll blow the cones, or burn out the voice coil. If you expect a 2-3 watt speaker. I'd say using a 5 watt amp would be a decent goal, requires an ear for clipping when you turn it up though, you'll hear the distortion when the speaker starts reaching it's physical boundaries long before the speaker blows as long as you don't feed it any bass spikes.