On your OLD account, go to the "Subscriptions" feed. Step 2: Create a new Public or Unlisted Playlist called "Channels to Move." Step 3: Go to each channel you want to keep. Click the three dots (⋮) next to the "Subscribe" button. Select "Add to playlist" and choose your "Channels to Move" playlist. Step 4: Switch to your NEW account. Open that playlist (you may need to send yourself the link). Step 5: Click on each channel name in the playlist description. This takes you to the channel page. Step 6: Hit "Subscribe."

Export the CSV via Google (safe), then use PocketTube just for the clicking (fast).

For most users, is the safest bet. If you have over 100 subscriptions, dedicate 15 minutes and a cup of coffee. If you have over 500, consider an automated extension—but vet it carefully.