The names that I see come up the most often are 
Rinkya, Celga, and Hobby Shop K.  There are 
others that I'm sure someone can testify about, 
and there are plusses and minuses for each of 
them.

Rinkya is by far the most expensive of the three 
services named above (high commissions, high 
fixed costs for things like the bank transfers 
and shipping).

I use Rinkya anyway, in spite of the expense, for 
a few reasons:

1. I'm a control freak.  Rinkya lets me bid when 
I want, as often as I want, however I want, even 
at the last second in auctions that don't have 
automatic extensions.  I get to see what the 
Celga and Hobby Shop K bidders have done hours 
before the auction ends, and am allowed to make 
my own strategy and tactics.  This is worth 
something to me.

2. They are credit-card based.  Celga requires 
use of PayPal.  (I think Hobby Shop K does as 
well).  I loathe PayPal, so it is worth something 
to me to be able to use a credit card for 
everything.  (My problem with PayPal is that I 
have a lifetime spending limit of $2K if I won't 
give them the keys to my bank account, and I 
refuse to give them the keys to my bank account)

3. I can bid against other bidders on the same 
deputy service;  that is, I can bid against other 
Rinkya people, as well as against Celga, etc. 
people.  With Celga, you cannot bid against 
another Celga person (even if you are willing to 
spend twice the money), unless that other Celga 
person is outbid by a non-Celga bidder.  This is 
worth something to me.

4. Rinkya lets me inspect closed YJP auctions.  
So that I can see, for example, that Yann won a 
cel a day or two ago that I was thinking about 
bidding on (but did not), which taught me that I 
probably should have bid on the cel, because Yann 
is a very smart guy;  lesson learned for next 
time from being able to do a post-mortem.

So, I spend more on commissions and costs at 
Rinkya, but I'm happy.  Your mileage may vary....