The most suitable reagent for the conversion of RCH2OH to RCHO is an oxidizing agent. Oxidation is a chemical reaction that involves the loss of electrons, and in this case, the primary alcohol (RCH2OH) is oxidized to an aldehyde (RCHO) by removing two hydrogen atoms.

There are several oxidizing agents that can be used for this conversion, but the choice depends on the desired reaction conditions and the nature of the alcohol being oxidized. Some commonly used oxidizing agents include:

1. Chromium trioxide (CrO3) in acidic medium:
- This reagent is commonly used for the oxidation of primary alcohols to aldehydes.
- The reaction takes place in the presence of a strong acid such as sulfuric acid (H2SO4) as a catalyst.
- The alcohol is mixed with the oxidizing agent and acid, and the reaction is carried out under reflux conditions (heating with continuous condensation of the reactants).
- The resulting aldehyde can be isolated by distillation or further oxidized to a carboxylic acid if desired.

2. Pyridinium chlorochromate (PCC):
- PCC is a milder and more selective oxidizing agent compared to chromium trioxide.
- It is commonly used for the oxidation of primary alcohols to aldehydes, especially when other functional groups are present that may be affected by stronger oxidizing agents.
- The reaction can be carried out at room temperature or under mild heating conditions.
- PCC is often used in organic synthesis due to its compatibility with various functional groups.

3. Jones reagent (chromic acid):
- Jones reagent is a mixture of chromic acid (H2CrO4) and sulfuric acid (H2SO4).
- It is a strong and efficient oxidizing agent used for the conversion of primary alcohols to aldehydes.
- The reaction is typically carried out under reflux conditions, and the resulting aldehyde can be isolated by distillation or further oxidized to a carboxylic acid.

In conclusion, the choice of oxidizing agent for the conversion of RCH2OH to RCHO depends on factors such as reaction conditions, desired selectivity, and the presence of other functional groups. Chromium trioxide in acidic medium, PCC, and Jones reagent are commonly used reagents for this transformation.