I doubt either scenario is very likely.
Take the USSR's OTL neighbours. Were all the communist parties in those neighbours more successful as a result of the USSR simply being there or was it due to active Soviet involvement? Also were any of those neighbours rabidly anti-communist again simply because the USSR was ther or because of active Soviet involvement?
Let's look at the OTL neighbours:
Afghanistan - Soviet Union was the first country to establish diplomatic relations with Afghanistan after the 1919 Anglo-Afghan War and the two countries signed a non-aggression pact in 1921 which apparently provided for transit rights for Afghanistan through the USSR.
Poland - Soviet Russia and Poland were at war in the 1920s.
Romania - there was a dispute over Bessarabia
Baltic States - not exactly "peace, love and harmony", but better than with Poland in a sense.
Finland - not very good after the Finnish Civil War which left Russia being equated with communism due to the support for the Finnish Reds. Border disputes didn't help the situation.
Mongolia - excellent. Mongolia followed in line as a puppet.
Tuva - see Mongolia.
Japan - indifferent after the Civil War in which Japan occupied portions of the Russian Far East including the Russian half of Sakhalin.
Persia/Iran - not hot following Imperial Russia's sphere of influence in northern Iran, followed by Communist Russia's support for communist rebellions in Persia in 1919-1920.
Turkey - so-so. Russia fought Turkey in World War I, but then the communist revolution brought about the Soviet Union which was more amenable to border changes in favour of Turkey in the Treaty of Kars. That treaty itself was a treaty of friendship which was an update on the earlier (1921) Treaty of Moscow.
China - pretty good after the civil war and until a minor conflict in 1929. So from 1921-1929 relations were decent as the USSR was supporting both the Chinese Communists and the Chinese Nationalists.
So essentially the USSR's neighbours fall into 4 broad categories:
1. Former Imperial Russian territories or countries which contained territory from Imperial Russia: Poland, Finland, Estonia, Latvia, Lithuania and Romania.
2. Countries with a negative experience of Imperial Russia and with Soviet support for communist uprisings: Iran/Persia
3. Countries with negligible negative experiences of Imperial and Communist Russia and which could potentially have decent relations with the USSR: China, Turkey, Japan, Afghanistan.
4. Countries which became communist allies: Mongolia and Tuva.
By the time any Czechoslovak-Soviet border is established (1921 at the earliest I would think) the revolutionary fervour has long since begun dying down in Europe and the prospects of any White v Red civil war in Czechoslovakia is nearly ASB (consider that despite having communist uprisings in Russia, Hungary and Germany as their neighbours, there was no serious communist uprising in Czechoslovakia except for the puppet communist Slovakia established by Bela Kun's Hungary). Not having been a part of the Russian Empire and having any real or perceived grievances against Russia and without any real or perceived grievances against communists (except Hungary) there wouldn't really be any basis for widespread hostility by Czechoslovakian society to the Soviet Union.
Likewise, a common border does not necessarily mean a stronger Czechoslovak communist party (think Japan, Afghanistan and Turkey) since that party still has to win votes and any increase in votes won due to material assistance is probably going to be small (maybe a 1-3% increase). Even so I doubt the USSR would be able to provide the kind of assistance that would swing large numbers of voters to the communist since the USSR is quite literally a mess after World War I, the Civil War and the border wars.
I also doubt the USSR would start demanding Carpathian Ruthenia. Just because the USSR did in 1945 doesn't mean it will in 1921 since the situations are completely different. In 1945 the USSR has it's armies steam rolling across Eastern Europe as part of a grand alliance and it can pretty much dictate what it wants. In the 1921 scenario envisaged here, the Soviet armies have managed to merely win control of the Curzon Line but haven't completely defeated Poland and are in no position to go towards Prague, Berlin or any other capital in Europe. Also, we should consider that despite having complete puppets in Tuva and Mongolia, the USSR made no attempt to annex them in 1921 or afterwards until 1944 when it annexed Tuva (again note the time: 1944...when the Soviet armies are poised to go into eastern Europe and the USSR is benefitting from a grand alliance). In 1921 the USSR is looking to make friends with just about anybody, which is why they cozied up to the Chinese communists AND the Chinese nationalists. It's also why the signed the Treaties of Moscow and Kars with Turkey and quickly recognized Afghanistan and signed a treaty with it.
What is more likely to have happened would the USSR signing a non-aggression pact with Czechoslovakia between 1921 and 1925 and also establishing diplomatic relations and a treaty of friendship. Relations would probably be okay (nothing spectacular but then not poisonous either) until any German resurgence. Should Germany follow it's OTL path then Munich would be very interesting. The Soviet Union would probably back Czechoslovakia and here they wouldn't need permission from Poland to provide assistance as they have a direct border. I could even see Emil Hácha or whoever happens to be Czechoslovakia's leader at the time giving Hitler the finger when it came to the Sudetenland and a war as a possible result.