After a month's trial, I'd have to say that SMJ still gets the nod from me. But here's what I found:
Auction browsing: Rinkya has the better search engine for finding a wider variety of things. I like being able to search for newer shows like Rozen Maiden and Samurai Champloo, which isn't possible with the rather limited search engine that YHJ gives.
Ease of bidding: about the same, though different. I found about the same number of bids-not-posted glitches on both services. (I suspect the problem is with YJ, not either DS.) And I appreciate the ability to bid in real-time, as I tend to bid late and bid high.
I also like the way that Rinkya notifies you if you're outbid by an external bidder. SMJ only does this if another SMJ user ups your bid.
I don't like the way that one Rinkya user can easily find out the identity of another Rinkya bidder and the exact amount of his/her reserve bid, making the likelihood of sniping and bidwars easier and more expensive.
Fees: with the sale I found them about the same on the low end, because Rinkya charges a flat $15 s/h fee at the time you're notified of your win, while SMJ itemizes and charges the exact postage/money transfer fee, which is almost always less than $15, sometimes substantially less. So even when Rinkya charged nothing for commission, the total price was about the same as SMJ with the commission. Obviously, now that the sale is off and Rinkya has gone back to adding a flat $15 commission (in addition to the $15 s/h), SMJ has a bigger advantage on lower priced items, as their commission is only $5 up to 1000 yen and $8 to 4000 yen. I'm a cheap SOB so this means a lot to me.
For larger ticket items, with the sale the Rinkya price seemed a little lower than SMJ, but this will disappear with Rinkya returning to normal in August.
Billing: Rinkya invoices winning bidders immediately after the win, and gives only 24 hours to pay up. PayPal or Credit Cards only. SMJ invoices winning bidders after the item is received in Japan, which can be just a day, or (in my experience) up to two weeks later. Then you have ten days to pay up, and can use either PayPal or a check or money order. The latter seems more customer-friendly. I also like that the invoice itemizes the exact cost of postage and wire transfer fees.
And, for a desperately hooked collector, a very important item .....
Getting your winnings to you: SMJ allows winners to track the progress of items from the seller to its Japanese facilities, to storage in the US. Generally, once an item shows up as RECEIVED J, it takes about a week for it to be RECEIVED A and be available for domestic shipping. At Rinkya, by contrast, items regularly sit at paidhold/jpseller (paid for, but not yet received [or, more likely, not yet processed] by Rinkya) for several weeks. It's impossible to tell where your items are in the meantime.
Recently, I won two items a week apart on YJ, the first on Rinkya, the second on SMJ. The first is still listed as paidhold/jpseller, while the second (won a week later) is RECEIVED A and now being shipped to me domestically.
Communications: Nick is good about responding to questions about the status of items and shipments, and has always responded within 24 hours, even in the case of silly questions. Rinkya makes you fill out a standardized form and isn't very encouraging about giving you any helpful response. I'm especially bemused by this notice:
(Worth noting that the Refund Policy provides only for the refund of the commission and states that Rinkya will "do their best" to get more back from the seller but can't guarantee anything more than this. By contrast, SMJ, as noted, does not invoice the buyer until the item is in their hands in Japan. So while there can be delays on that side, you are not asked to put the money up in advance and risk not getting it refunded if the seller is dishonest. SMJ also provides a pop-up warning at the time of bidding if a given seller has a history of being unreliable.)Please note, before submitting this form that items may take up to 1 month to arrive & be checked into the warehouse in Japan.
If your item has not arrived after 1 month from when you won it, please use this form.
ALL OTHER REQUESTS WILL BE IGNORED.
Please allow 7 days for your research inquiry to be answered.
If your seller still has not sent the item, please refer to our Refund Policy.
I'd say Rinkya shines on the auction-browsing front, is about the same on bidding, but is decidedly less convenient in invoicing and clearly inferior on customer service.
). 
Yes theyve had their problems, alot lately actually, which is why I chose to upgrade and get my own ID to eliminate the careless errors or mess-up's I was having before. Its worked beautifully 
-- althou Im thinking of switching out soon as well, because of lost auction items close friends of mine have been reporting about. I just dont wanna risk it on my end. 
