Ahh chorus pedals.
Right off I will state that in my opinion analog circuirtry is noticably better than digital when it comes to choruses (and echo units too for that matter). I prefer a very thick, lush effect when it comes to chorus, subtle ain't for me!
Probably one the best is the Analogman chorus. It is actually an improved version of the EH Small Clone.
http://www.analogman.com/clone.htm. With the "Deep" option is key for use with bass. It is a bit spendy. I am planning to get the Bi-chorus model.
I have tried the EH Clone Theory but found it too noisy an it still had the usual lowend dropout that so many choruses have when used with bass. It does do some really extreme "underwater" stuff that is fun though. There are a few newer EH units like the Neo Clone that I haven't tried and they have been working on improving the lowend integrity of many of their pedals (probably because of the trend of down tuning and 7+ string guitars) so it may be that these newer units are more bass-frendly.
The EH Poly Chorus is a really cool unit that has been around for a long time and I have debated getting one more than once but the thing that has always stopped me is that, like many EH pedals, it is almost too variable and minute adjustments to the knobs can have dramatic effects, so dialing it in (and then keeping it there) is not something I'd want in a live performance unit. It also takes up quite a bit of boardspace which is something I don't want to sacrifice to a mere chorus pedal.
I tried the Digitech Multi Voice chorus and did not like it, it was very digital sounding and there were noticable ghosting when the pedal was switched off. I have not tried their "Chorus Factory" pedal yet so can't speak to that one.
Another pedal I have been wanting to try is the Hardwire CR-7. But I have many positive reviews of it on the TB effects forum.
Likewise I have not sampled the Line6 units except for the old four switch unit and I remember not being favorable to that one. However, Line6 has been doing a lot to improve and innovate and the M9 and M13 multiFX units have been getting raves on TB and other places so I say give 'em a try.
I have tried all the Boss pedals even the much lauded MIJ Bass Chorus and didn't like them. In most cases it was because I could not get as deep, lush type of efect that I prefer, but many people use them. I have not had a chance to try out the twin pedal version or the Space Echo pedal yet but I have heard that they are better that the single pedal units.
Another good pedal is the old yellow MXR M-134 unit, it even does a fair job of retaining the lowend signal, I have been very tempted to pick up one of these and if I could find the right price on one still might. I have heard the new small cased unit is pretty good too but haven't tested it myself.
The HBE THC (Triple Hound Chorus) is a very good unit and comes closest to challenging the Analogman unit. I think that the Analogman with Deep is just a bit better, but it is a close call and I would be very satisfied with one on my board. It is in about the same price range.
The original Visual Sound H2O chorus/echo pedal was a good sounding unit, I don't know how well the new series compares.
As for what I actually use;
I have used an old 18v Danelectro Cool Cat for years. I really like this pedal because it seems to preserve my lowend better than most and it gets a very lush chorus which I most often prefer when using chorus. The only problem with the Dano pedals is the construction, The jacks are plastic and mount directly to the curcuit board, I have already killed one unit. The trick with these are to mount it to a pedalboard and leave it there. Otherwise, with the heavy die cast housing they are practically bombproof. The fact that it is no problem to find used units for about $35 doesn't hurt either!
Just be sure to use it with a power supply or you'll spend a fortune in 9v batties in no time!
Cheers!