Is it a sin to pray a Salat without Wudu even though he takes Wudu for the other 4 prayers? Which one is a lesser evil: praying Salat on time without Wudu or praying Salat late with Wudu?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Whoever performs the prayer knowing that he is not in the state of purity, no doubt such a person commits a great sin. So, he should make sincere repentance and should beg the Forgiveness of Allah.

Moreover, such a person should repeat all those prayers which he had performed without ablution. Tahaarah (ritual purity) is a basic condition for the validity of the prayer. Thus, a person must obtain the ritual purity and perform ablution for performing the prayer. Allah Says (what means): {And if you are in a state of janabah, then purify yourselves.} [Quran 5:6]
Moreover, the Prophet said: “Allah does not accept prayer without purification.” [Muslim]
In fact, the one who performs prayer without being in the state of purity is the same as the one who does not pray at all. Some scholars even believe that such a person becomes a disbeliever.

On the other hand, once a person performs ablution, he may perform as many prayers as he likes as long as the ablution is not nullified by one of its known nullifiers.

Allah knows best.