Checking express3 is a very interesting exercise
On Moscow-St Petersburg, there are unexpectedly quite many night trains, but it's getting a bit hard to make up my mind (apart than "Grand Express" which seems a bit overrated).
it is true for most cars of Grand Express, but not for all.
Grand Express apart their exclusive cars has alse some usual cars with relatively moderate prices - they are not so cheap as non-branded trains (but on this direction there are usually no non-branded train with good departure/arrival time), but cheaper than "Red Arrow" (well, it is normal, "Red Arrow" has special cars and higher price is normal) and cheaper than other branded trains (like train №4 and some others, which are often worse, tha those generic cars of Grand Express).
Which ones shall I favour?
Well if the price will suit you - I can propose you to try train №002 "Red Arrow". It has special cars wich has more space in kupe - such cars were made specially for "Red Arrow", they have 8 kupe per 25,5 m car while in other trains standard car has 9 kupe per 24,5 m car - so you'll get kupe which is ~17% breiter.
What is the difference between 1Б "Business" and 1Л "Deluxe" ?
Normally the difference is in meails and other additions. In 1Л there are no meals (it is basic fare), but 1Б has a "business class" set of meals and some other additions (newspapers, hygienic set). The number of sets (it can be important in long yourneys can be seen after letter У, for example У1 - is one set). 1Б with У0 is also possible - than means that no meals provided, but only those additions, which are normally provided when meals are included.
Which will be those meals - usually is unknown which addition - is also always a surprice.
In case of "Grand Express" you can look to their site, they give detailed list.
But for other trains you'll never know if you'll got as an addition..
But, as you can see, these included meals and additions increase the price very seriously,so I can recomend you try to get 1Л always when possbile.
The only one notice about "Grand Express" - you can find that one car is 1Л and unexpectively is more expensive than other 1Б (normally 1Л is of course cheaper). Such situation is possible because this is not usual l SV car, but special car (it has the same capacity as SV, but there are breit good beds)
http://grandexpress.ru/ru/kupe3.phpit is the reason why it is more expensive. Other 1Б cars are usual SV with narrow beds).