Transfection efficiency and the choice of the most appropriate method can vary greatly depending on the type of cells being used. Here are some examples of different cell types and how they can be transfected:

1. Eukaryotic Cell Lines: These are often the easiest to transfect and include commonly used cell lines such as HEK293 (human embryonic kidney cells) and HeLa (human cervical cancer cells). Transfection in these cells can often be achieved using a variety of methods, including lipofection, calcium phosphate transfection, or electroporation.
2. Primary Cells: These cells are taken directly from a living organism and are not immortalized like cell lines. Primary cells are typically more difficult to transfect. Electroporation or specialized transfection reagents designed for primary cells are often used.
3. Stem Cells: Pluripotent stem cells, including induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs), can be particularly challenging to transfect. Specialized transfection reagents or electroporation are often used, and optimization of transfection conditions is typically necessary.
4. Hard-to-Transfect Cells: Certain cell types, such as primary neurons, lymphocytes, and certain types of cancer cells, are notoriously difficult to transfect. In these cases, viral transduction or electroporation is often used, although these methods can also be more cytotoxic.
5. Bacteria and Yeast: Although technically not transfection (the term for bacteria is transformation and for yeast is transfection or transformation), DNA can also be introduced into bacteria and yeast cells. This is typically done using heat shock or electroporation.
6. Plant Cells: Plant cells have a cell wall that makes transfection more challenging. Methods such as Agrobacterium-mediated transformation or biolistics (gene gun) are often used.

Remember, the most effective transfection method can vary not only based on the cell type but also depending on factors such as the size and type of DNA being transfected, the desired level of expression, and whether transient or stable expression is desired. It’s often necessary to try multiple methods and optimize conditions to achieve the best results.