It's hard to say whether Upper Attack is better than Smash Attack in HMS, imo. Circle and Samurai Upper are both better Attack Rings overall than Jiraiya Blade, for example, but in terms of pure Attack, it's hard to say. There's so many variables. Like poseidon said, it's probably a better idea to use Smash Attack in TB against a Bearing Core combo. However, against a Bearing Core 2 combo, you'd probably want to use Upper Attack.
In TBTS, Upper Attack is the way to go against Bearing Core and Bearing Core 2 combos, but at the same time, if you're sure that you're going to be facing an Upper Attack type (which is pretty likely in TBTS, I would say!), Smash is a good choice. Lets say I chose Jiraiya Blade; it absolutely
wrecks for Smash. It would do well enough against Bearing Core combos if your opponent was stupid enough to use one in TBTS, but it would also likely do well against Upper Attack combos. Because Upper Attack can only work properly if both Beyblades are spinning in the same spin direction, it becomes harder to use in HMS because you do not know what spin direction your opponent will choose. Smash works the same in either direction, so the uncontrollable variable/problem of your opponents spin direction selection is eliminated. You could just use Slash Upper though–as it has both Smash
and Upper–but you'd be sacrificing both weight and attack range.
Ga'Hooleone, I'm not sure what you're saying about Tornado Attack is true. I don't own Tornado Attack, but as far as I know, it doesn't favour Stamina combos to the same degree that TB does; it's much more balanced.
All of this HMS talk is making me want to bust them out and start doing testing again!