If you believe that they will win in game 1, trust them to cover the spread. Currently, the Moneyline (ML) odds for the Nuggets are only 1.28, so I think that is too low for gambling unless you have great faith in them and would like to bet a decent amount. However, if you're not betting a lot of money, I think -10 with odds of 2.03 would be fine. Sometimes we have doubts about whether the spread will be covered, but often, when we have doubts, it's the easiest bet that we should take.
In the end, you just have to be confident and trust your analysis.
Money line is not that sweet because the Denver Nuggets now are listed as a very heavy favorite because of what seed they've finished the regular season plus they have pulled a stunt that very few can make and that was sweeping a team in a conference finals. So, if you're looking a heavy payout, handicap will be needed but giving a +10 advantage on the Heat might be a bad choice. Nobody can guarantee that of course, so who knows what will happen on their first game.
Ya, this is a case where it seems pretty clear that Denver is going to take game 1. They're more well rested, Jimmy Buckets has an ankle injury, Denver is younger, Denver is playing at home in the mile high city, Denver matches up well against Butler and Bam, Denver had a better season, Denver has been playing together longer as a team, etc...
That leaves pretty bum odds to bet against. I'd almost say it's worth taking the Heat to win with the given odds, but I honestly don't think they have much of a chance. Jokic will shut down Bam, MPJ & BGordon will shut down Butler, and Murray will absolutely go off against Miami's guards. I see Denver winning this series in 5.