In Jain Dharma, none of these should be seen as “small” — all three are very important:

• Samayik: practice of equanimity, inner peace, and self-control
• Brahmacharya: restraint and purity, a very strong vow
• Upvas: fasting, an austerity that helps reduce attachment to the body and senses

If you mean spiritually which is greater, then samayik is often regarded as very high, because it directly develops samyak bhav and equanimity, which is the essence of Jain practice. But brahmacharya is also extremely important, and upvas supports spiritual purification.

So the best Jain answer is:

Samayik is the core of inner discipline, brahmacharya is a major vow of restraint, and upvas is a powerful austerity — all three are श्रेष्ठ in their own place.