This is a very easy question to answer as Portia is by far the most interesting and definitely the most reliable character compared to Jessica. Jessica is an interesting character in the way that she can be portrayed incredibly negatively in the play. Note how when she elopes with Lorenzo, she doesn't just escape, but also steals his riches. Likewise, when they engage on their honeymoon spree, she is rumoured to have exchanged a turquoise ring belonging to her mother for a monkey. It is clear that what her father treasured and held dear, she squanders without a thought for her father's feelings. Note what Shylock says about the ring she exchanged for a monkey:
It was my turquoise; I had it of Leah when I was a bachelor. I would not have given it for a wilderness of monkeys.
Such scenes allow Jessica to be presented not as a daughter escaping the harsh life her father inflicts on her but as a callous, unthinking and cruel daughter.
She is quick to convert to Christianity and leave her father's faith behind her, and all of these characteristics question her reliability and also cast doubts upon the kind of character she is.
Portia, however, is certainly reliable. Once she has married Bassanio, she is willing to spend all of her fortune to help Antonio escape his fate. She remains constant to Bassanio and his friends, even engineering the release of Antonio herself, recognising her husband's inability to help Antonio himself. This arguably makes her a fascinating Shakespearian heroine, as she is shown to be superior to the male characters and directs them in her play which she carefully stage manages.
Therefore, considering Jessica and Portia, it is clear that Portia is by far the most interesting and reliable in the play. Jessica is at best only a minor character, and the text raises severe questions about her reliability and characteristics.
ofcourse portia, jessica iz also a v.interesting but portia iz much reliable than jessica.