I need a grille for doing mainly chicken, there is an inkling to buy a gas grille but I heard charcoal grilles are better for flavour, I like the convenience of gas, but flavour is compelling, is this true?
There are many advantages to gas: better heat control, easier to clean, less potentially carcinogenic soot.
In my experience, the flavor that can be imparted by charcoal is superior, especially with good charcoal like that sold at Trader Joes.
However, I have not tried any of the wood slabs that are meant for use with grilling. Perhaps these have some effect on the difference.
Because of the differences others have mentioned, I actually own both. I prefer the taste of charcoal but just don't have the time or energy for charcoal sometimes.
My main grill is a gas grill, which is very large, convenient and easy to use. I can have grilled chicken go from fridge to plate in about 15 minutes, including prep, without having to do almost any work at all. I also have a smoker box for when I want to use wood chips in the gas grill. I also sometimes cook on wood planks in my gas grill, such as salmon on cedar. As johnny mentioned, when I have a large amount of guests, I find it much easier to work with my gas grill.
Then, for when I have the time or energy, such as when I have a couple guests over for a nice steak on a Saturday, I pull out my small, cheap charcoal grill and chimney starter (which heats the coals faster and more evenly).
I'm a big charcoal advocate. You can get higher temperatures from charcoal, and a good grill (read: Weber kettle) offers a great deal of flexibility. It's easier to deal with flare-ups, and once you attain a good skill level you can have more consistent temperatures across your cooking surface. Plus, it tastes better.
Once I started using lump charcoal and a chimney starter, I have been able to get up and running a lot quicker. Usually I'll start a chimney full of coals, then do my prep work on the food. Within 10-15 minutes, the coals are ready for cooking (using Kingsford briquettes, it's more like 20-25).
However, I find the biggest benefit to be the use of indirect heat. You can use a gasser to cook food indirectly, but it's just not designed to do cooks that way, making for a very inefficient cooking method. I've used my big gas grill in the past, but it uses a lot of propane, and a lot of heat escapes from under the hood. The kettle, on the other hand, is designed to convect heat. Particularly for roasting/barbecuing at somewhat higher temps (350F+), charcoal is the way to go.
Overall, I recommend having both. Spend 100 less dollars on whatever gas grill you want to buy, and complement it with a Weber One Touch Silver (80 bucks for the 22") or something comparable.