There's also a hard rubber Conn I just found, is hard rubber preferable to Grenadilla?

 

The Leblanc or Conn would be good, safe bets on getting a decent bass. I would be a little hesitant to go with the Willclar unless it came with a really good return policy.

As for grenadilla vs. hard rubber... It's all a matter of personal preferance and maintainance.
Both will sound like a bass clarinet.
Wood requires a bit more care, and is not something you would want to subject to extreme weather conditions/temps.
Hard rubber is better if you plan on doing a lot of outdoor gigs.

 

I was surprised by the $200 shipping on the Leblanc:

2. Leblanc- http://cgi.ebay.com/Leblanc-Profess...47905053QQcmdZViewItemQQptZLH_DefaultDomain_2?hash=item3359adf61d#ht_899wt_1093

The "search forum" tool is your friend in this case for finding advice. I've been thinking about this too and have bookmarked these Doubling/clarinet threads:

Help-Me-Choose-Please- Bass-Clarinet
WTB-cheap-bass-clarinet
Inexpensive-bass-clarinet

Several are old but I still found the information useful. Also look in the "Marketplace/Ebay experiences" section. At least a few recent bass clarinets on ebay have been from sellers for whom SOTW members reported poor experiences in that forum.

 

The biggest thing to look for on a bass clarinet is a "double" register mechanism - think similar to the octave mechanism on a saxophone - because with the size of a BC, the single position of a traditional register vent just is not adequate to produce a consistent scale and intonation.

A maker who has made the effort to incorporate this style of mechanism is generally concerned about their instruments. My bass clarinet is a Malerne stencil, very similar to the Conn pictured. It's an excellent horn, although since the upper register pip is on the neck, a bit more of a challenge to keep adjusted.

Looking at the horns listed, I'd rate them 1. Conn, 2. Leblanc, 3. Willclar, although I admit I've been watching that willclar curiously.

 

The biggest thing to look for on a bass clarinet is a "double" register mechanism - think similar to the octave mechanism on a saxophone - because with the size of a BC, the single position of a traditional register vent just is not adequate to produce a consistent scale and intonation.

I disagree. It is true that the best bass clarinets have this mechanism. However there are some very good, relatively inexpensive student models, like the Yamaha 221II, which play very good even with just one register key. On the other hand, the absolutely worst bass clarinet I've ever played had the double register mech, made of wood too. Some older single-reg-mech bass clarinets are also decent. To get a good bass clarinet with double-reg-mech is a lot more expensive usually