If you are really playing 1-base in SC2 all the time i'm guessing your protoss or rather low placed in the ladder.
The only game i havent played online, is CoH. But that doesn't matter because CoH has easily the best singleplayer experience (CoH>SC2>SupCom).
TBH you cant really compare the games. Sure they are all RTS but everyone is focusing on a different aspect. Starcraft is hard on the macro and game mechanic side. If you cant keep up the production and your macro you're going to loose vs someone who can. SupCom is about map control and tactical decision when it comes to unit movement. I guess CoH is realy affected by its "special" eco system and is about deciding when and where to engage and capture a specific target, positioning yourself for that fight etc..
The one thing i can say about SC2 vs SupCom is which one is better supported. IIRC FA-beta Players where mostly high rated 1v1 player like Bluescreen or Loui. And you can see that FA has a great balance for 1v1 on 5x5/10x10 maps. But as soon as you hit t3, you see all this unfinished and unbalanced stuff (T3 Air OP, T3 land UP vs exp (buildtime), T3 arty, useless exp etc. etc.). I have not seen one thing in SC2 that is as utterly useless as a Novax.
SC2 had a lot of feedback and an active Dev with a huge bank. Thats why its the better game for esports. SupCom had this great UI idea and then a medi-core Dev with not much money. Vanilla was not a good game imo. They never really could change it and made it even worse with t2 bots. I guess they reacted to alot of feedback for FA because its basically a complete overhaul and made the game rather good.
And thats why i think SC2 is the better game. It's better balanced and plays better. You have 3 different Races that actually play different (not 3 times the same with a different model and fire animation) and a huge sucess in esports that allow for entertainment. I don't enjoy playing it though because i feel out of control with my low skill.
There's only one reason why i enjoy playin SupCom. That is large scale T1/T2/T3 battles over all of the map to fight for +2 mass income while you zoom out and can control everything. Or in words from the internet:
Supreme Commander is an insane clusterfuck of an RTS which has skyrocketed to fame in the RTS community for what is apparently it's only redeeming quality: the Strategic Zoom feature.
FAF said it would endorse change to SupCom, thats why i startetd playing again and hoping for the future that all these big issues are someday getting tackled, despite the huge resistance that some might have to changing the game just because it has been in this (poorly) state the last 4 years.