Before anyone ventures down a path of interpreting that the Noble is not a stellar piece of kit, let me say it absolutely is. It sounds great and is amazingly well built. The DI alone sounds great. Adding in EQ makes it more versatile. I have no doubt it would great in a mix and take a bass guitar signal and make it sound, well, better. If you want an easy-to-use device that is about as plug-and-play as it gets, the Noble is on a different level than many (most) other preamp pedals I've tried.
The RNDI sounds just as good to me as the Noble without EQ applied. If I had to pick a favorite, I'd give the edge to the RNDI for straight DI signal because to my ear it adds a sweetness to the highs that the Noble doesn't. Everything else is quite equal. But I doubt that's why most people buy the Noble. They want a sweet DI signal with the ability to tweak the tone too. But it doesn't really offer the tube sound I was looking for in a tube preamp.
The Oracle can be dialed in to sound pretty much just like the Noble but offers far more in the way of tone tweaking including being more aggressive, offering more complexity in mids (and mid control), and having more of the "tube tone" we assume a tube device would have. Which is better between the Noble and Oracle? For me, the decision is easily the Oracle. Maybe not for you. This is especially true if you just want to plug in and go. The Noble offers the 9 volt outputs to power other pedals which may be enticing to you. The fact that these outputs are not isolated means that this is not an attractive feature for me. The Oracle does lack a XLR out though which might be a deal breaker for some.
Then there is the Grace Alix. It is not a tube preamp. But it sounds just as full and big, if not more so than either the Oracle or Noble because it has this bottomless feel to it. It has more of a 3D complexity than either the Oracle or Noble. It isn't a tube hairiness, no its just something sweet and spacial. Maybe it is the transformer. It is easily the most versatile with full sweepable HPF, phase reversing (the magic button), fully sweepable mids (and selectable in which range), sweepable Q, Notch filter (if you want), and impedance selection. The XLR is ridiculously quiet. Those features matter to me. Maybe not you. For a non-tube preamp it has a complexity of sound I've never experienced. The Trickfish Trilobite is similar but the phase reversal switch and mid Q allows you to make the Grace Alix have a very focused, punchy, solid state type of pristine sound, or roll it off for a wider, looser, more tube type experience. The impedance selection makes the Grace Alix a tone machine for anything from high output active basses to passive basses to upright basses with piezo systems. Then you have other features I will likely never use like the 12 volt phantom power out. The Alix also has a 9volt output to power other pedals. The Mute footswitch is important to me. I appreciate having the Tuner out which allows me to keep the tuner pedal out of the signal path. I appreciate the line level and mic level selection for the DI out. I appreciate the up to 10db boost option with footswitch to activate when a slight boost is needed (such as on choruses or situations where a little more gain is needed to "keep up").
Circling back to the Noble, there is a reason you don't see many on the used market. It's very, very nice for what it is.
