.com is the king, the reference, the extension that every end user/investor/domainer wants.
Every powerful/great/prospect .com is taken; every .com dropping is monitored; new trend keywords are monitored: the .com domain market is completely saturated.
I'm not saying that buying a .com domain is not a good investment.
I suggest that buying a good reg fee .com domain or buying a good .com at auction at the right price is very hard for a BEGINNER. So the chance of making a mistake when buying a .com is high.
Different story for the other TLDs especially the new TLDs. The market is still immature, more space for new investors. It is still a risk, but if the market takes off, it is easier to make a profit. Of course, if the market does not take off in the short term, the renewal costs could eat up all the capital, but every investment has its own risks.
I'm a beginner. I want to buy a reg fee domain for $12.
What is available as .com? A short name that is unthinkable or a 3-word domain name? As a novice investor, I have to ask myself ten times why that .com domain is still available.
On the other side. I'm a beginner. I want to buy a reg fee domain for $12 with a new TLD. I can buy a dictionary_name + new TLD. You are buying a great name (may be will never sell) but for sure it's not a bad name. You are betting your entire investment on the fact that this new TLD will be successful because the dictionary name is not under discussion.