Any dry red wine will work in a tomato-based spaghetti sauce, with each varietal imparting unique flavors. While it may be tempting to use an inexpensive cooking wine, the flavor of the wine will, however subtly, shine through in the sauce. A good rule of thumb to follow is: if you wouldn't drink it, don't cook with it.
The flavors present in a wine will become more concentrated as they cook. Keep this in mind when choosing a wine to add to spaghetti sauce. Stay away from overly tannic wines, such as those made with Cabernet Sauvignon or Nebbiolo, as the tannins will add harsh, astringent qualities to your sauce. Unless you are looking to add bright, fruity flavors, you may want to avoid wines made with Gamay or Zinfandel. Look for a medium-bodied, well-balanced, dry red wine with an interesting flavor profile.
It makes sense that an Italian wine works with an Italian dish. The best wine to use in spaghetti sauce is Chianti, or any wine made from Sangiovese grapes. Its moderate tannins and full range of flavors, from cherry to leaves to tobacco and sometimes mushroom, add depth of flavor to any red sauce.
Pinot Noir's subtly nuanced flavors, usually a mix of fragrant red fruit and earth, are lovely to cook with because they won't overwhelm most ingredients, even when reduced to a high concentration. Pinot Noir can sometimes exhibit flavors of mushroom, which works well in savory dishes.
While it can sometimes be on the higher end of the tannic spectrum, Syrah's flavor profile makes it an undeniably intriguing wine to cook with. Syrah generally possesses a strong pepper element, paired with a unique smoked or gamey meat quality. A savory or spicy spaghetti sauce, particularly one with beef or boar, would benefit from the addition of Syrah.
While Merlot wines can sometimes be thin and overly fruity, this is not always the case. A well-crafted Merlot can exhibit strong black fruit flavors as well as roasted flavors and aromas like cocoa, coffee, and spice. Along with its moderate tannic structure, these characteristics make it an appropriate and interesting ingredient in spaghetti sauce.
A wonderful wine to use in cooking, Cabernet Franc is medium-bodied. It lacks much of a tannic structure but shares similar flavors and aromas with Cabernet Sauvignon. It is more delicate but tends to exhibit similar earthy and herbaceous aromas, while tending more toward red fruit than black. Cooking this wine concentrates its delicate flavors, making them more pronounced but not overwhelmingly so.