In most settings, halflings are smaller and weaker than medium-sized folk, but known for their agility and pro-social communities. They are most often creatures of comfort thrust into the role of adventurers, and likely to play comic-relief in a light-hearted story.
In most cases, an abilen is the ideal replacement for a halfling. Their mechanical strengths and weaknesses are quite similar, and they are likewise associated with community values, common sense, luck, good humour and material comforts.
Kobolds and felbraug are also worth considering. These occupy a less similar flavour niche, but they match the small stature and nimble nature of the halflings. Mechanically, both offer similar appeal to the fan-favoured halfling rogue.
Finally, if you enjoy the comedy variants of halflings (and similar folk like the notorious kender), the gremblin (Almish goblin) may be quite appealing. A small species themed around family and community values, gremblins also have a cultural view of ownership that encourages you to filch anything you need (from those who can afford it).