The Weber Attenuators aren't that great. They really change the sound when you use very low volume compared to some of the newer ones.
The Phantom Attenuator is supposed to currently be the best but I wouldn't know as they have some people waiting over a year to get theirs due to the demand and the price is about $1,000. There's no way that I'd pay (I think they ask for half the money for a deposit) and then wait for over a year while the company solves their issues with parts suppliers etc.
The Alex Attenuator is pretty good. It's not my favorite though. When I have to play at bedroom levels because I often play when everyone is sleeping, I use the Ho Attenuator. Some people don't like the Ho because it puts a big load on the amp's tubes. I haven't had a problem with mine.
There are better ones out these these days probably but for now I'm good.
You have to make sure you get an attenuator that can handle all the volume coming out of the amp.
When a guitar amp (for example) is rated at 100 Watts, that means 100 Watts of clean signal. Once you turn up a 100 watt amp to the point where it is distorting, it can be actually putting out 200 watts.
I don't have any experience with using an attenuator for bass though.
I just did a quick search on youtube and found this: