Traditionally, in all Sephardic communities, the most common Shofar is the ram's Shofar. Lately, however, the 'antelope' horn, which is 3 to 4 times longer than a ram's Shofar became very popular. Probably because it is easier to blow than the ram's Shofar and it has a beautiful 'deep' sound.
Can we use the 'antelope' Shofar for Rosh haShana? Our sages mentioned the ram's horn as the ideal Shofar for Rosh haShana, because on Rosh haShana we also remember akedat Yitzchak (the binding of Yitzchak). Abraham found a ram 'caught in the thicket by its horns', which he then offered it as a sacrifice in place of Yitzchak.
Now, is the ram's horn the only Shofar suitable for Rosh haShana or the best one?
According to Maimonides, we can use only a ram's horn for Rosh haShana and all other Shofarot are invalid. The Shulchan Arukh took a more lenient approach, saying that a ram's horn is preferable to any other Shofar, but other Shofarot are acceptable too.
On Rosh haShana -when listening to the Shofar is a Mitzvah from the Torah- we should use exclusively a ram's Shofar. If for any reason, no ram's Shofar is available, then we could use other Shofarot.
For the Tekiot that we perform during Selichot and for the Terua Gedola at the end of Yom Kippur, any Shofar is acceptable.