It's always safer to show an under construction/contact us kind of page.
The word "always" is a dangerous word.
What you said above is correct:
having the domain parked and showing competitors ads is almost 100% certain to be called Bad Faith
Most of the time that's true, assuming that the alleged mark is actually distinctive.
But I wouldn't agree that an "under construction / contact us kind of page" is always safer.
With words that are dictionary terms, non-distinctive descriptive phrases, geographic terms, etc. you are much safer if they are
appropriately parked.
And the reason for that is because a lot of dictionary terms, etc., happen to be trademarks. So you have two scenarios when you are dealing with a dictionary word like "TIDE", which is a famous mark for detergent:
1. An under construction page / contact us page.
2. A parking page with things like weather forecasts, boat navigational equipment, surfboards, etc.
Now, let's say that someone contacted you to purchase the name and you quoted them $X. It turns out they are the TM owner and they file a UDRP. Their complaint says, "We have this trademark, the respondent isn't doing anything with the domain name, and they want $X to sell it to us."
Your defense is, "It's a dictionary word, and I didn't register it and seek to sell it because it was a trademark."
What is going to be more helpful evidence in your favor? The situation described as 1, in which the domain name is not used for anything; or the situation described as 2, in which the domain name is clearly being used for things that have to do with the dictionary meaning of the word "tide"?
Obviously, all things being equal, you are much better off with the parking page relating to the word "tide", because nobody has to simply take your word for it that you did not have the trademark in mind. In that situation, the parking page itself is evidence of non-infringing use and intent.