Found the buses from Chișinău to Odesa (http://www.garanord.md/orarul_rutelor.cfm?S_ORAS=Odesa&ID=20910&CODU=208937&Grid1Page=1), though why do only the later buses in the day state Palanca?
in fact palanca mentioned after dash in destination point (for example ODESA/PALANCA(GA)) - is optional.
If destination point don't contain this /PALANCA it doesn't mean bus doesn't go via Palanca.
Simply one bus carrier insisted their departure should be listed with explicit mentioning of going via Palance, other bus carrier didn't this and bus station simply list Odessa.
I know you stated most buses will avoid Transnistria (though I will have already visited there on the trip), just wasn't sure if these buses go through there or not? Doesn't really say anything on the website.
it's wrong impression. Most of buses go via Palanca. Most of those, which are listed as simply to odessa and those where explicitly written via Palanca or via Tudora (it's the same way).
With present stupid design of Garanord.md website you can ensure the bus you like really go via Palanca only by making separate seach to Palanca http://www.garanord.md/orarul_rutelor.cfm?S_ORAS=palanca&ID=20822#ruta1
and findining in results all buses which you've seen in search result to Odessa. As you can see - almost all buses are here - morning, daytime and evening.
Does that just means there's an official stop there while the early buses in the day just drive through Palanca and not stop?
It means only garanord.md website could be better. It so stupid that their database "knows" intermediate stops, but don't allow to see them by clicking the departure.
but yes, the problem that intermediate point Vama Palanca is listed in one bus departure and missed in other, despite both go via Palanca - is possible too.
you can also try MAIACHI AS, STEFAN-VODA, STAROCAZ+, CAUSENI. If at last one of those intermediate point is present in bus route and then bus reaches Odessa - bus definitely bypasses Transnistria.
As for Odesa-Kyiv, found I can book the train 2 weeks in advance
well, 1st class is not a big problem, Ukrainians almost don't buy it while seat of 2nd class are available, because find it too pricey. Only when 2nd class is gone - seats in 1st class start to sold-out quickly.
and that the first class will get me to Kyiv at a decent time in the day and only seems to be 1/2 shorter than the bus (unless like mentioned the buses drive faster in the day than the time stated).
Let me explain once more, may be it's will be more clear this way.
Daytime train takes 7 hours.
Convenient buses (the most of buses, I don't reccomend to use them) - have official travel time varying from 7:00 (and can be up to 8 hours), de-facto travel takes usually ~6:45. Comfort level - definitely worse than 2nd class in train. Try to avoid them if there is better option.
But there are few the fastest and more comfortable buses (not all Autolux and Gunsel ones, but only very few particular ones - the 6:00, 16:00 and 18:35 Autolux and 5:45 and 17:15 Gunsel) - have listed travel time 6:30, de-facto travel time will be ~5-5,5 hours. The bus which used for this departures provide higher level of comfort than normal bus, for example here is one type of coaches which used on such departures of Autoluxhttp://www.unvertur.com/images/safir_vip.jpg
there is only 28 seats (instead of standar 45) in 12-meter bus, seats stand 2+1 instead of 2+2 and more space between rows. Comfort level definitely better than 2nd class of train.
Those few particular bus departures (5 per day in current timetable) - are the only buses I've proposed you to think about.
Might be more comfortable on the train as first class opposed to the bus...
But of course, in case of comparsion with 1st class in train - bus is worse, even such better one. In train there is more space. Rolling stock used for daytime train Odessa - Kyiv have 3,5 meters wide carbodies and in 1st class there is 2+2 seats. Definitely 2+2 seats in 3,5 meter wide car-body provide more space than 2+1 seat in 2,5 meter-wide bus.