s.MP x EX tackle comes in handy against MGB and other stuff from far away. Using EX headbutt instead of the tackle doesn’t work against a lot of smaller characters. Personally I have bad experiences using s.MP x EX headbutt, on Ken it often just hits once for some reason and I don’t get the juggle. At the closest range, s.MP x MK tackle is good when a c.HP isn’t viable, does more damage than LK tackle (in comparison LK tackle can combo from a bit further away). Sometimes I just do straight up LK tackle if I feel nothing else will hit from the range I’m at and I don’t want to use meter.
If you have time but you’re not that close, you could always cancel the first hit of a low fierce (pretty decent range on the first hit depending on character hitbox) into a headbutt or HK tackle. But usually if this is possible, there’s something better to choose from.
Typically I avoid using EX moves much against Chun, Yun, and various others in non-punishment situations. Use your own judgment depending on round, health, meter, character, range, etc.