This is entirely dependant on the metagame you're playing in. And also on the current format (that is, Forbidden and Limited List).
if your metagame highly favors decks that destroy many monsters by effects, even face-down ones, Morphing Jar is not a good idea because it will often be destroyed before even getting the chance to flip for its effect.
If your metagame favors fast swarming decks that can do insane amounts of damage in a single turn, Morphing Jar is a bad idea because it will often take the spot of a card that might have saved you, while he only lay there and stopped one attack, which wasn't enough to save you from losing.
If you metagame favors many Set Cards or decks that play out their hands almost every turn, Morphing Jar is a double-edged Card because on the one hand, it can really help you in getting a new hand after playing everything down, but on the other hand, it can help your opponent even more if they just played out their entire hand and get a fresh 5 Cards essentially for free.
If your metagame favors slow setup decks that collect combos or do little for several turns, Morphing Jar is generally a good idea because it will have disruptive power and might just survive into your turn so you can play down your entire hand and Flip Summon it to get the most out of its effect.
If your metagame is full of Dark World decks, Morphing Jar is a terrible idea. Read any Dark World Monster and you will know why.
Bottom line, Morphing Jar is one of those general Cards that are only as good as the metagame they're in and depend much more on those circumstances than on the deck you're playing.
Watch what decks others are playing and how typical turns play out, then think about the impact a Set Morphing Jar would have. If you do that for many different (but common) situations, you will get a very good feeling of how well Morphing Jar fits into your metagame.