Ken:
The relative small market for LS trains, batch rather than continuous production and a supply chain that in most cases stretches to China causes lots of availability uncertainties, delays and missed deliveries. Each person seems to have their favorite source, but there is no single source that has the best prices, everything in stock, and will make their shipping schedules 100%.
Another wrinkle is that the shop with the best price sometimes has the highest shipping and handling charge, thus negating part of the low price. Be certain you understand what additional charges are involved before giving them your CC.
I'm certain the next 10 posts will sight deficiencies with (insert supplier name) and give assurance that (insert supplier name) has never missed a delivery, but in my opinion they are all about the same. I would encourage you to find the best way to contact whatever supplier(s) you choose. This can access the best information to trace items that are slow in getting to your RR. Simply sending a supplier an email is usually the way to get ignored.
Just one example: I have found Bachmann service to be good, but emails and / or phone calls to their 800 number often go unanswered or do not produce a result. Calling their regular business number during their East Coast office hours does get good results.
Most of the large on-line vendors are good when it comes to getting a set, car or other large packaged items off the shelf and sending it to you. Getting scratchbuild and other small parts is often more difficult. I do trade with Wholesale Trains and have found them to be good in all respects, even getting some items (trucks) they did not have in stock and that were no longer being manufactured. It just took a while, but no one else offered to get the parts, so waiting was the only way to get the result I wanted.
'The Bachmann' (moderator of Bachmann's forum site) has a single word saying: "Anticipate". That about summarizes the LS train market.
Happy RRing,
Jerry