The Helghast are "mostly harmless". They are a pain in the sector of space they live in, but they tend to have limited ambitions in regards to their ends. The Covanent happened to invade earth and did major mayhem. They are a greater problem, and more of headache to deal with. Of course, we could get into the Flood. The Flood vs both of these is a MAJOR problem. Not sure how long the Helghast would hold out if they faced The Flood.

Besides, I believe the Helghast got the short end of the stick.

There are different types http://img19.imageshack.us/img19/2223/helghast.jpg

I haven't played the halo story so I don't know much about the covenant, but the story for the Helghast people is fitting and is pretty cool.
But I don't know anything about the covenant lol.

covenant

Helghast. when I play they look the same to me : dead!

Helghast, just because the Helghast Sinper looks so fking badass!

Results will be posted by tonight!

Helghast... by far IMO, for many reasons people posted...

Oh and Heavy Helghast FTW!

@ Mendicate---Thanks for my new desktop background!  Where did you find such a sweet pic?

OT: Covenant, They have invisability, alot have sheilds, they have all sorts of really powerfull weapons, their numbers are so much greater than the Helghan, and they can glass a planet from orbit withought breaking a sweat.  So yeah Helghan don't stand even a 1% chance against the covenant...

The Covenant.
Grunts make me laugh.

Helghast

The convenant are just some silly blind sheep evil alien, but the helghast could have been the good guy's in killzone which make them more deep then the convenant since there's no black and white only shades of gray