Last spring, I flew to Germany to reunite with my husband after his military deployment. We splurged on an upgrade to the most premium class available for our flight home, spending an extra $699 each for Delta One.

The lie-flat seat was a luxury on our 10-hour flight, and the service was fantastic, but our plane seemed a bit outdated and worn. From the clunky entertainment system to the lack of privacy between seats, I felt our nearly-20-year-old aircraft showed its age.

We got elevated meals, amenity kits, and complimentary alcohol, but I expected more features or perks considering a Delta One upgrade often costs thousands of dollars.

Although our experience fell short of my expectations, I still think the upgrade was worth paying for to celebrate such a special occasion.

In the future, I would only justify the cost of Delta One if I knew I'd be on a newer plane with more state-of-the-art amenities. After all, some newer Delta One classes have suites with doors.

When returning from Europe last winter, my husband and I upgraded to Premium Select seats for $209 each on our nine-hour flight.

Premium Select upgrades are primarily offered on long-haul flights and come with early boarding (although my status already gets me into the same boarding group that this would).

We enjoyed the added legroom and additional recline of our seats, which made them noticeably more comfortable. The upgraded dining, larger entertainment screens, and in-flight amenity kits also elevated the experience.

However, we upgraded at the last minute, so our seat options were limited. Unfortunately, I ended up sandwiched in the middle seat next to a stranger. In hindsight, I wish I'd saved the money and kept my window seat in economy.

Being crammed in a middle seat for nine hours took away from the premium experience. Next time, I'd try to upgrade earlier so I could choose a better seat.

Overall, Premium Select strikes a solid balance between affordability and comfort with its thoughtful amenities and extra space. However, it's not always available on Delta flights, and I'd likely skip it if I couldn't get a spot next to a window.

A step above economy, Delta's Comfort Plus provides slightly more legroom and priority boarding. For domestic itineraries, this class also receives alcoholic drinks and a better selection of snacks.

With my status, I've received many complimentary upgrades to Comfort Plus.

Last fall, I flew in Comfort Plus from Seoul to Atlanta after one such free upgrade. As a tall woman, the extra legroom was an added bonus, especially on a 13-hour flight.

However, I've found you can get about the same amount of legroom in an economy exit row for a more affordable price.

I'm happy to accept a free upgrade to Comfort Plus, but I wouldn't pay extra for these seats, which I've seen cost $100 or more than economy.

And, on international routes, Comfort Plus receives many of the same in-flight amenities as the rest of the main cabin. That said, Comfort Plus does get reserved overhead bin space, which is always nice on a fully booked flight.

Most of my Delta flights have been in economy class, including long-haul flights to Africa, Europe, Asia, and Australia.

Although some complain about economy seats, I actually prefer choosing this affordable option. For starters, Delta's main cabin offers more seat choices, which gives me flexibility.

I can almost always snag my preferred seat next to a window, where I can lean on the side of the plane to sleep during the flight.

Plus, I often monitor the seating chart before international flights, and like that I can move near an empty row or seat whenever possible.

Although some also consider basic economy to be a cabin category, its seats are still in the main cabin, you just can't choose where you sit (and there are limitations with changing and canceling your trip).

I'd rather be able to select my seat before my flight instead of saving a few bucks.

Overall, I'd rather book a cheaper flight so I can spend money elsewhere on my trip.

A flight is just one of the many costs of a vacation. I also need to pay for accommodations, additional transportation, meals, and activities.

By booking affordable economy flights, I have more money to travel more often — and that's always my goal. Plus, I can almost always secure my beloved window seat if I book my trip far enough in advance.

However, I'm definitely still open to enjoying the occasional upgrade if the price, plane, and time feel right.

"I think the etiquette is that first class is about indulgence," Ott told Business Insider.

Ott doesn't recommend asking flight attendants whether each bonus offering is free because everything is complimentary, from meals to sparkling wine.

And there's nothing wrong with "filling your boots" to make the most of the perks, he added.

While first-class passengers often get personalized experiences and are greeted by name, business-class flyers shouldn't expect the same level of attention.

"Business class is about efficiency. It's a comfortable seat where you can sleep or work," Ott said.

Staff members serve dozens of people in business class, while first-class cabins typically seat fewer than 10 passengers, he added.

"There's a lot of work that goes into all those meals and drinks," Ott said. "So if you're looking for an over-the-top experience, then first class is where you can expect staff to make the flight awesome. And that's what you're paying for."

If you've flown recently, you may have noticed that many business- and first-class cabins have added doors to each seat to give passengers more privacy.

Ott said you shouldn't infringe on another traveler's space to fetch items from overhead bins.

"Don't awkwardly hover over the person because the whole idea of doors is that people can't look in on you," Ott said. "So when you wake up and someone is looking over your space, it's odd."

BI previously reported that premium-cabin passengers are often entitled to overhead-bin space, and according to Ott, the bins are usually not too crowded. But that doesn't mean you should bring extra bags and put them wherever you want, as Ott has seen many passengers do.

Instead, Ott suggests keeping your limited belongings in the space above your seat.