Live Plants
I confess I still have a penchant for live plants. Nothing matches the pride one feels in displaying a well crafted aquarium of live plants. However pride isn't the primary reason I prefer live plants. I believe live plants provide a more natural habitat for fish and offer benefits that cannot be duplicated by artificial plants.

Unlike their plastic counterparts, live plants grow and respire

During daylight hours they take in carbon dioxide and give off oxygen, thus contributing to a healthy habitat. Keep in mind that at night this process reverses. In heavily planted tanks carbon dioxide levels can rise significantly, while the oxygen levels drop off. If fish are observed hanging close to the top of the water and gasp for air, it may be necessary to run an airstone at night.

Live plants harbor bacteria that aid in the breakdown of wastes. A well maintained planted aquarium often needs little chemical filtration. However there is a flip side to the coin. If plants decay and the debris is not removed quickly, they can produce waste that is harmful to the fish. Further, it is possible for live plants to carry harmful pests such as snails, and parasites that cause disease.

Plastic is inedible, but live plants can be a tasty meal for your fish. This is especially helpful if keeping fish that are herbivores, as they require frequent feedings. Live plants also make the aquarium look appealing, and can inhibit algae growth by reducing nitrates. On the downside, plants that are nibbled on extensively can detract from the appearance of the aquarium.

Pros

• Absorbs CO2 (in daylight)
   
• Gives off O2 (in daylight)
   
• Absorbs toxins
   
• Harbors beneficial bacteria
   
• Serves as food source
   
• Inhibits algae growth

Cons

• Can cause O2 deficiency at night
   
• Creates waste when decayed
   
• Can carry parasites
   
• Not easy to clean
   
• Requires good lighting

Artificial Plants
Artificial plants have become so sophisticated that they rival real plants in appearance. Unlike live plants, they will not die, grow too large, or become tattered and unattractive. If they become dirty or covered with algae, they can easily be removed and cleaned. Artificial plants have no light requirements, as opposed to live plants which often require lighting beyond what the average fish keeper has for their aquarium.

Silk and plastic plants come in a wide range of sizes and colors, and are easily obtainable year round. Because they are never in an aquarium before you purchase them, they will not bring in pests or parasites from other places. They will not decay and foul the tank. Granted, they will also not contribute to the habitat in the way live plants do, but they are an excellent option - especially for the beginner. Artificial plants are also an ideal choice for fish that are prone to uproot or eat live plants.

Pros

• Does not affects O2 levels
   
• Does not create wastes
   
• Does not carry parasites
   
• Easily removed and cleaned
   
• Does not need special lighting

Cons

• Does not absorb CO2
   
• Does not give off O2
   
• Does not absorb toxins
   
• Does not carry bacteria
   
• Cannot be used as food source
   
• Doesn't inhibit algae growth

As you can see there are plenty of pros and cons for each option. A well planned and maintained aquarium can be beautiful with either real or artificial plants. Ultimately it's up to the personal preference of the owner.