Abu Hassan is an iconic hummus restaurant popular with tourists and locals alike. There are several locations, all intended for a lunch time crowd; in other words, the restaurants are closed by late afternoon.
The location in Jaffa offers a charming setting on winding, stone walled streets. The space is small and you should expect to sit with strangers that quickly become friendly acquaintances as you all delight in the delicious hummus.
The staff is pleasant and the line moves relatively quickly. The diners consist of older locals and younger backpackers. All enjoy the hummus bowl with raw onion.
I suggest you get the combination hummus platter so you get to try multiple types and, if you can tolerate spice, ask for it.
This is a great place to walk to from Tel Aviv along the promenade on a nice day. It is inexpensive, tasty, and a bit of an authentic experience of a traditional middle eastern lunch.