But, on stage I bring my own D.I.s (this is a good habit everyone should have...) and I also have a pretty thorough experience with D.I.s in general. So, barring using the front panel input of a thousand or more dollar mic pre, here are my three choices for D.I. boxes, low, medium, and high-end:
GOOD: Countryman Type 85. $159 a throw. This is the standard the world over for stage D.I.; if you're a musician that needs to D.I. an instrument when you play live, and you're not rolling in cash, you should own one (or more) of these. Personally, I have 8. You literally can't go wrong with a Countryman. Another nice bonus is that if you show up to the gig with your own D.I.s, and they're these, the soundman (assuming he isn't a complete asstard) will automatically assume you know what you're doing, whether you do or not. (Note: sometimes the soundman will try to steal these from you when he's wrapping the stage. Make sure yours are well-marked, and you grab them literally before you do _anything_ else. The single most commonly stolen item in the music industry is the Type 85. How do you think I got 8 of 'em?)
BETTER: D.W. Fearn Passive Direct Box $300. Unless you have techs that will guard your shit, you generally don't want to be taking anything more expensive than that Countryman on stage, unless it's bolted in your rack. Thus, this isn't that good an idea for that particular course of action, as it's tiny and easily stolen. But if you need a good D.I. in your studio, you could do worse than this box. The thing is that in order to really see any benefit over the Type 85, you need a good mic pre to grab the info from this fucker, and if you have a good mic pre, it probably has an instrument input, which kind of obviates something like this. So it's in a hazy grey area. But I've used it, and it doesn't suck, not one bit. Handy if you have racked console pres, and they don't have instrument inputs.
BETTERER: Avalon U5. $575. Now we're getting in to heavy duty territory. The thing about the U5 isn't that it'll make your shit sound better than it already does. (In fact, its clarity will bring to light maybe some things you didn't want to hear, like fret buzz, hiss in your analog synth, and the like.) Rather, the U5 is the most eminently controllable D.I. made. It can grab pretty much any signal coming down a 1/4" cable and turn it in to something an Apogee can swallow whole. The best feature is that it has a power-soak input, so you can plug the speaker output from a guitar or bass head directly in to it. This is quite handy in today's home studio. I won't say it sounds great, as it doesn't sound at all. One of the most color-free devices made. If you're looking for an all-around studio D.I. that will absolutely be able to do whatever you ask of it without altering the input in the slightest, this is the box for you. Well worth the money.
BEST: Tab-Funkenwerk V71. $750. This is a D.I. made using the topology of everyone's favorite tube mic pre, the Telefunken V72. Absolutely the best thing going for bass D.I. If you want something that will fatten up the input, and give it some nice overtones, this is the box for you. Stellar for vintage analog synths, as well. Now, a caveat: if I was you, and I was looking at this box, I would just save a little more money and buy the TAB-Funkewerk V78 mic pre and a Countryman. Same net effect, but the V78 is a mic pre, and thus more useful in general.
As far as I'm concerned, the above are all one needs to know about D.I. boxes. What's stated is my opinion only, based on my personal experience.