I've played TA, Generals, C&C 3, and Supreme Commander (demo).
In general, C&C 3 is much much faster than Supreme Commander. Usually, matches (even 2v2 with brutal AIs) end under 15 minute tops. For me, the superweapon goes up around 3 mins into the game, but usually when I get the chance to use it, the battle has already a clear winner. Matches are very much action-focused, with less strategy and more quick witt and click-frenzy. Big battles occur 5-10minutes into the game, and beyond 10minutes most/all of the resource fields are used up, and resource regeneration rate in the game is painfully slow.
On the other hand, Supreme Commander is slower to start and much more focused on strategy. Complicated orders can be executed, such as ferrying, flanking, coordinating, patrolling/waypointing, etc. There are also much more units and the scale is much larger. It actually takes time to get to an enemy's base while in C&C, you're about 1-2 screens away. Once you get your resource going, SupCom also picks up the pace better, and battles get more and more frenzied as time goes on. Also, radar, shields, experimental units, nukes gives SupCom much more strategical options.
All in all, play C&C if you want a quick game of limited thinking. All you gotta do is pump out units quick and send them over to the enemy. The storyline is good, but skirmish has limited replay value. Play SupCom if you have at least 1-2hrs to devote to a good game, and be prepared to use real strategy. In my humble opinion, it takes a lot more skill to ace at SupCom than C&C, and SupCom is the better game, but C&C works on lesser comps and is a fairly good dumbed down RTS in it's own right.
About the predator tank strategy though... I'm a little doubtful that it would work, as brutal AI sends a mix of APC/missile squads/predator tanks to your base at around the 2-3minute mark. 1 predator tank defending probably isn't going to cut it... I find that a few missile squads, snipers, and mammoths work decent as a defense line, with maybe some zone troopers thrown in. However, if the AI sends in his 16+ orcas.....