HELOC on primary residence vs Mortgage to purchase rental

[Lawrence S.]

My questions is as above. 

I have a HELOC on a primary residence at prime.

I am also approved for a 30 year fixed conventional mortgage at 2.89%.

The HELOC and loan are the same amount.

I am getting mixed messages on which to use. Some are saying HELOC is better because of its simple interest/average daily interest versus conventional has compound interest.

I am thinking conventional mortgage is better b/c of lower fixed rate with no variability. I will be paying extra monthly in either scenario.

Any advice would be greatly appreciated!