One of you asked this question today, so here is the complicated answer. Since I play Puppet Stayman over 2NT openings, I can open 2NT even with a 5-card major, because partner can find out whether I have a 4 OR 5-card major. (Of course, if I have a 5=4=2=2 hand, I am more likely to open the major and jump shift second time around.)
In terms of 1NT openings, I mostly follow Eddie Kantar's suggestions. So, all 17 HCP hands are opened one of the major and I jump to 2NT for my rebid (or rebid 2NT over partner's forcing 1NT call). This shows 18-19 ostensibly, but you are adding a point for your (decent) 5-card suit.
Eddie suggests that the 15-16 hands can be opened 1♠ and you'll be fine most of the time, but 1NT is more likely to shut out the opponents when your major is hearts. This is something to consider in terms of matchpoint strategy.
I look at the overall hand. If my suit is poor, e.g., Kxxxx or worse, I will open 1NT. If I have a worthless doubleton, I will usually open the major. If I have a lot of tenaces, I will open the NT because I want the lead coming into my hand. (Example would be ♠KJxxx ♥AQ ♦Kxx ♣Kxx. With three Kings, I definitely want to play the no trump from my side of the table—opening 1♠ would risk partner becoming the NT Declarer.)
The main reason to open 1NT is that you can have a rebid problem over 1 of a major/pass/1NT by your partner. 2NT would show the 18-19 HCP hand, so how do you invite? This is much more of a problem playing Standard American than 2 over 1. The reason is, with 2 over 1, Opener will bid a “convenient” minor and Responder will usually take a “false preference” back to the major with 2-card support; or change suits (“Don't write; don't call.”); or raise the convenient minor; or bid 2NT. So, Opener will often have a second chance to further define the hand. This is not true, however, when partner is a passed hand. 1NT by Responder is NOT forcing one round by a passed hand, so some of your options are gone. So, I'm more likely to open the NT opposite a passed hand.
In Standard American, Opener will often pass the 1NT response (whether passed or unpassed hand) and you will sometimes miss game when partner has a good 9 or 10 HCPs. So, playing Standard American, I would be much more likely to open 1NT most of the time. Playing two over one, I would feel comfortable opening the major most of the time—again bearing in mind the points above.