@tara85,
First things first:
"Would" has different usages".--"usages" is plural, while "a" is singular. Additionally, the first word of all sentences must be capitalized.
In this case, "would" establishes the condition of "most convenient," and therefore, one uses the conditional form of the verb to be, which is would. One clue to this is the use of "were" in the subsequent clause, which is the subjunctive. (The subjunctive is much neglected, and I suspect that many native speakers these days don't even know what it is.)