Grenadiers are one of the most important units in Red Alert online play, especially in 1v1 matches and on maps like P4 where there is lots of money and open spaces for you to cause damage. They are also almost essential on maps like Keep off the Grass and Pico. They are also a viable strategy on maps such as Path Beyond and North By Northwest where you could even go 2 ore refineries before your 1st War factory in order to maintain your economy and finish the game with overwhelming naders. They are extremely effective against power plants and ore refineries as well as rifle infantry.
I actually see Grenadiers as one of the most skillful aspects of the game as using the Scatter (X) and Stop (S) keys are fundamental in addition to mouse clicking and scouting. You can truly see the skill of certain opponents when facing their grenadiers.
Here are the players who I consider to be the 5 best Grenadier users I have encountered. Some honourable mentions to Nastynate, Hezb, Otto, Katsh and Robskate:
5) Sol3|MAN|
A Finnish expert player who patented the Grenadiers into 4 tanks into Cying P4 build. You see Nastynate do a variant of this play today but Sol3 truly perfected it. His timing was excellent and he had his build nailed. A very strong opponent.
4) Ifuc
Ifuc would nade on every map and he had excellent unit control, even able to beat Ehy on occasion 1v1 and on maps like P4 and 4c his naders wouldn't let you sleep 1v1.
3) Bea5ty
Amazing nader control which is usually followed up by a quick rush or some quick CYs.
2) Herm [aka Rushyboo]
A true wizard and his grenadier use is probably just as strong as his famous soviet building. He would be number 1 if not for the Tiberian Dawn expert who is next.
1) Lovehandles
A genius. Anyone who has played Lovehandles on KOTG knows he can run rings round you. He rarely plays Red Alert, preferring to play other C&C games where he is as far as I'm aware the undisputed best player on Tiberian Dawn, but when he shows up he beats platinum challenge without breaking sweat and demolishes anyone who dares play him on KOTG and other maps. Just ask players such as Ford and RC about Lovehandles' naders. His unit micro in general is unequalled. Example video of his play below: