White worms are a great food for most tropical fish. As a rule, any fish will try to ingest anything moving that it can fit in it's mouth. White worms prefer a cool/cold for keeping. Grindal worms are very different. Much smaller and need warm conditions if you want to keep for fish feeding. Both are fatty so feed in moderation. More like a treat than a regular diet. If you wanted to choose between the two, I would go with grindals, espcially if your fish are small to medium size.