This question is often discussed even among bicycle racers and top professionals, and the correct answer of an "expert cyclist" is often based on half truths, false assumptions and failure to understand basic facts.  In reality the answer to this question is not straightforward and generally valid, because it depends on how the bicycle and tire will be used.  Therefore, only general facts with characteristics of available tire types will be listed here:

• Are used by the majority of competitive Cyclists
• From all tire types tubular tires have the lowest rolling resistance
• Tubular tires are the lightest
• Tubular rims are lighter than clincher rims
• Higher air pressures are possible with tubulars than with clincher type tires
  
• In case of a flat the stability and safety of the rider is not affected as much as in the case with clincher tires
• Tubular tires can be ridden flat in case of an emergency
• It is necessary to glue tubular tires to the rim
• Flat repairs are not easy ( this does not apply to TUFO tubular tires when TUFO sealant is used, and in many cases the repair is instant)

Clincher Tires:

• Clincher tires are the heaviest of all choices of bicycle tires
  
• It is necessary to use an inner tube which adds weight and lowers rolling resistance
  
• It is necessary to use a rim liner which adds more weight
  
• Clincher tires are heavier than tubular tires
  
• Clincher tires have a higher rolling resistance than tubular tires
  
• In case of a flat, the repair is possible but not easy, and in some cases the tube must be replaced
  
• Installation is not easy and in most cases tools are required, also care is needed not to pinch the tube
  
• You can ride on the repaired or newly installed tire immediately
  
• In case of a flat, there is an instant affect on the stability and safety of the rider
  
• Instant contact of the metal rim and the pavement can result in a fall

Tufo Tubular Tires for Clincher Rims:

• Tufo has developed a totally new and revolutionary construction for tires
• Low rolling resistance
• There is no need for a rim liner
• Low weight
• There is no need for glue
• This is the easiest and fastest installation for all types of tires, no tools required
• Higher air pressure is possible
• In case of a flat the stability of the bicycle is not compromised as much as a normal clincher tire and provides better stability and less danger of a fall
• In case of an emergency the tire can be ridden flat
• The tire can be ridden immediately after installation
• The construction and compactness are equal to tubular tires and the riding properties are very close to tubular tires as well  
  

Summary:

For racing purposes and quality training, or for a ride with feeling of lightness, tubular tires are the obvious choice.  Their main advantage is the significant saving in weight, not only on the tire itself, but also on the rim.  This weight savings can amount to 500 grams for the combined front and rear wheels.  Moreover, the weight savings is realized on the circumference, or outside parts of the wheels.  So, from a physical point in the case of acceleration the lower weight is far more important than the weight of any other part of the bicycle.
 
It is important to understand that races are won by acceleration at the right and critical moment, as in the final sprint, catching up to the peloton, and in a breakaway.
 
At the same time, low rolling resistance and safety in case of flats are strong arguments for tubular tires.  TUFO tubular clincher tires have a universal appeal.  They can be used anywhere tubular or clincher tires are used (road races, time trials, training, cyclocross, mountain biking, and touring.
 
For those who switch from clincher tires to tubular clinchers there is no extra cost.  Indeed, the tubular clincher tire does not need an inertube or rim liner.  One will soon realize the advantage of easy installation and, in combination with TUFO sealant, the fastest and most effective flat repair without removing the tire form the rim.