There have been several good ways to portray Gnomes.
Eberroni, despite the fact I don't really care for it, has some
amazing fluff regarding gnomes, IMO. Secret police keeping everyone in line? That's pretty sweet!
Forgotten Realms Has the Svifneblin, Rock and Forest varieties, and doesn't really do much to switch 'em up. The coolest bit of gnome-lore are the... well, here's the text, "At present the worst such group is the Blood Screamers, a band of savage gnome dire weremoles led by a gnome vampire called Blood-Curdling Scream (CE male rock gnome vampire illusionist 9). This group supposedly lairs in a warren of tunnels dug by giant ants...." Not their typical representation, but I love this plot hook
DragonLance had the silly tinker gnomes. The best part about this was the "mad" gnomes whose inventions actually worked.

that was funny, but I still don't think these are a great representation of gnomes.
By core, gnomes are bland, and IMO, they need some major change-ups in regards to favoured class. Rock Gnomes need Beguiler or Illusionist. Period. Forest Gnomes get druid, obviously. Deep Gnomes should prolly get illusionist or Beguiler too.
But, despite Eberroni's great fluff, I prefer to bring the gnomes back to their roots as a earth-flavoured fey creature. They are not a playable race in my Ascension campaign setting, but another one of the fey-folk, fairies, etc that inhabit my world. That's their niche, and they will even sometimes hang around dwarves in their tunnels helping them out, but it's not like they are a core race or anything IMC.
Personally, though I like Forest gnomes out of core the best. They fit the fey archetype and actually bring a divine-magic class into the fray as a favoured class for one of the core races.
Also, one last note on gnomes, rock gnomes in particular: I am really dissapointed that they got rid of the +2 Int, -2 Wis from AD&D. Personally, I think this got rid of a lot of potential flavour for gnomes, which is dissapointing.