Way back in my 1st edition AD&D days, I felt like I had a pretty solid grasp on what halflings were all about -- rustic generally good-natured little people whose natural talents (and lack of fortitude) inclined them towards stealthy careers as adventurers. If they weren't off killing owlbears then they were largely honest and competent farmers, craftsmen, etc. The hobbit thing didn't bother me much, possibly because I was never much of a Tolkien reader so it wasn't beaten into the ground for me.

Gnomes, in contrast, I never felt like I could really explain. Sort of dwarfish but thinner and they like jokes? Something something small animals? And I guess they like magic but just illusion magic. I could sort of grasp them as individuals but I never felt like I could picture what a gnome settlement or society looked like. This is just based off the PHB; I didn't really have the primary campaign world supplements.

Krynn sort of changed that but it did so by wiping out most of the PHB info: No jokes, no magic illusions, no something something small animals. Just obnoxious steampunk dwarfs. No thanks. Then you have your fae-style gnomes or rock spirit gnomes, etc.

My favorite depiction of gnomes came form the Paksenarrion novels where they were a hyper-lawful austere people whose plain, perfectly engineered tunnels contrasted with the gem-encrusted and decorative stoneworks of the dwarfs. Measure for measure, anything done for you was assumed to have a price and almost nothing was done for others freely. But expert fighters and tacticians, keepers of law and knowledge. Again, this is little like the 1st edition PHB but at least it was a society concept I could work with.

Anyway, out of the two I'd easily keep halflings. With halflings, I know where I'm at mentally. Gnomes fluctuate so much that I have to consider them as disposable because they've never found a concrete role.