Make one of the rooms take 2-3 people per guild per spar, and the other require 4-5. There is nothing as boring as being on either end of a 5 vs 2 match.

Edit:
A few people I talked to thought it would also be cool to have a room where the winning guild stayed on.  

make it winner stays on or refactor the queue every time a new team joins so that it puts bigger teams at the beggining of the queue and matches them against the team with the size closest to their own

as in, if one team of 5, one team of 4, and two teams of 2 queue at the same time, it will ensure that 5 vs. 4 and 2 vs. 2 occurs
nothing is more boring than sparring 5 vs. 2  

In one of Graalians numerous guild spar threads, I suggested that the guild spar queue should be edited to match guilds for fair 2v2 3v3 4v4 5v5 fights. It also gets boring sparring the same guild over and over because theres an even number of guilds in the room and the queue is linear.