The correct sentence is OUR GROUP IS THE BEST OF THE LOT. The term "OUR GROUP" is in a singular form, it means the group as a whole or as one. Therefore, the verb must also be in singular form to follow the rule of subject-verb agreement. Use of are and were is incorrect because both are in plural form despite their different tenses. am is used when an individual is talking about him or herself.
Which sentence uses the verb correctly? Our group are the best of the lot. Our group is the best of the lot. Our group were the best of the lot. Our group am the best of the lot.