Our software update is now concluded. You will need to reset your password to log in. In order to do this, you will have to click "Log in" in the top right corner and then "Forgot your password?".
Welcome to PokéCommunity! Register now and join one of the best fan communities on the 'net to talk Pokémon and more! We are not affiliated with The Pokémon Company or Nintendo.
Yeah, Diglett's Cave and Pokemon Tower look like the best places at that point of the game.
Later, I can recommend Cinnabar Mansion, the lower levels of Seafoam Islands (surprisingly easy to reach and exit) and of course Victory Road.
Apart from that, there's too many Pidgey and Rattata line members (who obviously don't exactly give good exp) around. Even in the patch of grass with Tangelas that becomes a grinding paradise in FRLG.
I grind in Route 18 (just below Cycling Road, west of Fuschia) IIRC, the Fearow and Doduo give decent experience. I prefer it to the Route 14/15 east of Fuschia. Diglett's Cave is also good because of the chance you run into Dugtrio (and thankfully they don't have Arena Trap in case things go south lol)
If it's between 4th and 5th badge, you won't be able to Surf; therefore Seafoam and Cinnabar are off limits for you currently.