This must be an April Fools Day question as it has been posted more times than I can remember and a quick search will turn up the answer (though some wrong ones will turn up too).
So again, the BEST method to degass any HPLC mobile phase is continuous sparging with high purity helium. Period. Do not turn it On, then OFF. Continuous sparging maintains the level of gas in the solution. Helium is not soluble in the mobile phase (which is what you want since we are not trying to turn the mobile phase into a fizzy drink. Never use nitrogen or argon). Helium displaces oxygen in the liquid (which vacuum and sonication methods do not). Displacing oxygen reduces low UV absorbance (if you are running in the low UV range, that is a good thing) and is also best for most Fluor det methods (quenching effects). Helium sparging may be more expensive, but it is THE BEST method.
Sonicating and or vacuum flask methods are better than nothing, but as soon as you take the solutions off the apparatus, the gas goes right back into the solution. This usually appears as baseline drift up or down over time. Not recommended for any validated or critical methods.
In-line electronic HPLC vacuum degassers provide a great deal of convenience in that they can maintain the level of degassing at a stable level over time (which equals a stable baseline). You just plug them in to operate, no tanks to order, exchange or hook up. However, the vacuum channels in modern degassers may have high internal volumes (lots of flushing and wasted solvent); are flow rate sensitive (the higher the flow rate, the lower the degassing efficiency) chemical compatibility problems (THF, methylene chloride, some strong acids, sodium azide, fluorinated solvents and/or Hexanes are not compatible with some models. **We see damaged vacuum degassers every week which have been used with inappropriate solvents and/or not serviced properly); pervaporation problems (esp with aqueous phases which can and do result in the destruction of the degasser components); and internal contamination of the mobile phase when used with incompatible liquids and/or operating too long without being serviced (a very common reason for failure and may result in very expensive contamination of MS sources). - So while they are super convenient to use, that convenience comes at a cost. As with anything, you must consider YOUR own applications, resources and needs in selecting the best method to us.