This is one of those ‘it depends’ answers but looking beyond that, there are certain factors that need to be taken into consideration when giving a finitive answer…
So to understand that answer, I will give a very quick history in the use of modern commercial gymnasiums – with the Arnold Schwarzenegger movie ‘Pumping Iron’ which showed in cinemas in the 1970s, came a revolution in the design and use of gymnasiums. A huge number of gymnasiums opened up around the world after that which catered for the general population. To cope with the increasing number of gym goers there was the development and usage of machine resistance equipment. Because this type of equipment was easy to use, most gym goers used this equipment exclusively (and still do in these gyms). Because there were limitations in design, most of this equipment only exercises specific body parts and even individual muscle groups. So the emphasis was taken away from natural movement and a lot of this type of machine equipment places undue stress on the joints (because the loading is on one joint, instead of sharing the loading over several joints).
This is only covers the very basic concept as to why this development took place. Only very recently that the emphasis was taken away from the exclusive use of this equipment to the more natural movements in the advent of Cross Fit gyms. Although I agree with the concept, in practice these gyms still cater for large numbers of people and push greater intensity by increasing the volumes of repetitions to the detriment of emphasizing correct technique.
The upshot of the use of both these modes of strength training is that there are a large number of unnecessary injuries – great business for the paramedical industry – but unnecessary none-the-less!
So, the short answer as to what are the best exercises to use in resistance programs are the ones that have more natural movement patterns and work the whole body for the most part. Even though these exercises encompass some of the oldest exercises known to man (if we use the same analogy that just like ancient medical practices are old) it doesn’t mean that they are obsolete! So exercises such as Squats; the various Jumps; Press Ups; Pull Ups; the many ‘Swinging’ movements (and the myriad combinations of these movements – such as the pictured example above, the Burpee) are ancient, natural movements (and therefore relate to everyday movements including the various movements in sports), but they are the most effective exercises to use for the majority of gym goers.
Combining these movements intensifies the program – if that is what is required? Some people may say that the various ‘Olympic Lifting’ movements would be more effective in producing the desired results, but these movements require expert advice and supervision. (May I add here, that a basic interest in these exercises doesn’t constitute ‘expert’?)
All the examples of what I consider the ‘best’ exercises mentioned above require no or very little equipment. To intensify these movements, they can be done using a single limb at a time (although I am not suggesting trying to do a Press Up or Pull Up this way – unless you are at the ‘elite’ level of ability?!) Adding a set of Dumbbells though, multiplies the variety of movements you can do.