Jack and Algernon are similar in that they are both determined and committed to please the women they love. For instance, they are both willing and even make plans with the Reverend to change their names to Ernest so they can be accepted by the women they love.
They are both escapists, as seen when they create fictitious characters in order to avoid facing tough circumstances. Algernon invents Bunbury, a fictitious friend, so he can always have a reason to escape his aunt, Augusta. On the other hand, Jack invents a fictitious brother named Ernest, to facilitate his escape from Cecily and her governess.
The difference between the two emanates from their different upbringing. Jack was raised by a benefactor who found him abandoned at the station while Algernon was raised by his aristocratic family.