HELOC: interest only vs interest + principal

[Susan Lee]

I’m a newbie and I’d love some opinions on which might be preferable and why. we’re trying to decide btw 2 credit unions, both have great rates, no fees, etc  this would be to buy our first flip. 

we can get a HELOC for $300k, no appraisal, 3 week processing time, and would have to pay interest + principal.

OR…

A HELOC for $300K, pay $750 for an appraisal, 2 months to process, but only pay interest for the first 5 yr.

I have two different concerns…having higher holding costs in the first scenario if things go a little sideways. In the second scenario, there’s the appraisal fee and longer processing time.

We aren't looking for deals yet, waiting to get the HELOC locked down.

I so appreciate any help. Thank you!