Hardest gold medal to get?

Dragon Tamer...still bronze.

In the top grouping, Tiny Rats! I always seem to catch Giant rats!
In the bottom grouping, Steel. I'm only at 64/200.

I have the least progress on Dragon Tamer (16/50), after that Fisherman (24/50). Ice types are not so common for me either with 46/50 on Skier. Those are the only bronze medals I have left. Everything else silver or higher.

Ofc unknown. It is even hard to get a bronze

all gold except the following are silver.
Top group: Tiny Rat and Pikachu.
Bottom group: Ice

(have yet to see/catch an unown)

Pikachus is a hard one. I can spend a whole month without encountering one !
Currently level 38, I miss Pika, Magikarp, Unown (of course) and Dragon (120/200).

Top: Fisherman (134/300), Ace Trainer (402/1000), Youngster (55/300), Pikachu Fan (94/300)
Bottom: Steel (111/200).

And I do not even have an Unown medal

I would have to say the magikarp or rat badge. It took me 2500 rat catches to get the gold. Still need 180+ karps. After that it depends on your areas biome. Those that live and work near the oceans will always have plenty of karp and dratini to catch.

It is interesting seeing the answers here and how everyone's biome is so different.

I will likely never get the dragon one - sitting at 20 right now. Also only 49 big magikarp. We don't really have any water here so these will take forever.

But I have had gold for 300 Pikachu for quite sometime. I don't even bother catching Pikachu anymore. I have nearly 1000 Pikachu candies and 7 82%+ ones ready to evolve at some point.

But man what I would give for Dratini or Magikarps to spawn here more often.

Ice is the rarest type in my biome.

Ice and steel medals are still silver for me as well as the pikachu medal.
Bronze is the dragon one and the gym related ones as well as the rattata and magikarp medals
And of course the one medal I doubt ill ever complete is the unown one which i have yet to see.

My only five that are still bronze are 15 dragon, 21 ice, 24 steel, 29 Magikarp (out of 221 caught), and 31 fighting.

Pikachu Gold

The last 3 took awhile for me....tiny rats, magikarp, then ice in that order

Unown will definitely be the hardest one.

The bottom rows are not that hard if you live in major city with lots of nests. My last one in this group was Dark type, but just because it was just added after Gen 2. Before that the Ice medal was really hard until there were a few ice nests showed up (Jynx, Sneasel, Swinub)

For the top rows apart from Unown, the Tiny rats was the last one for me. The Pikachu fan would be really hard without the nest/events.