When considering reliable, comfortable, and valuable used luxury cars, it's essential to focus on models with a strong reputation for longevity, comfort, and retaining value. Here are some top choices:

1. Lexus LS
Reliability: Known for its bulletproof reliability, the Lexus LS often ranks top in terms of long-term dependability.
Comfort: The LS offers a smooth and quiet ride with a luxurious interior of high-end materials and features.
Value: Although new models are expensive, used Lexus LS models offer great value due to their lower depreciation rate than other luxury sedans.

2. Mercedes-Benz E-Class
Reliability: The E-Class is a benchmark for mid-size luxury, with newer models offering improved reliability.
Comfort: Known for its plush interior, advanced technology, and comfortable ride, the E-Class is ideal for long drives.
Value: The E-Class retains value well, especially models with the AMG trim or diesel engines, which are sought after in the used market.

3. BMW 5 Series
Reliability: The 5 Series has a solid reputation, particularly with models that have been well-maintained.
Comfort: BMW's 5 Series is known for its balance of comfort and sportiness, providing an engaging driving experience without compromising luxury.
Value: Older 5 Series models are reasonably priced, making them a great value for those seeking a luxury experience.

4. Audi A6
Reliability: The Audi A6 is generally reliable, especially with regular maintenance.
Comfort: Offers a quiet, well-appointed cabin with advanced tech features and a comfortable ride.
Value: The A6 tends to depreciate faster than some competitors, making used models a bargain for luxury car buyers.

5. Acura RLX
Reliability: Acura vehicles are known for longevity, and the RLX is no exception.
Comfort: The RLX offers a smooth ride with a spacious interior and high-quality materials.
Value: With lower initial pricing than some European rivals, a used RLX can offer exceptional value in the luxury market.

6. Jaguar XF
Reliability: While older models had issues, recent models have improved reliability ratings.
Comfort: The XF stands out for its luxurious interior, comfortable seating, and distinctive styling.
Value: Jaguars tend to depreciate faster than German competitors, making a used XF a more affordable luxury option.

7. Volvo S90
Reliability: Volvo is known for building safe and durable cars; the S90 is no exception.
Comfort: The S90 offers a Scandinavian minimalist design, comfortable seats, and a serene driving experience.
Value: Volvo’s strong focus on safety and comfort makes the S90 a good value in the used luxury market.

8. Porsche Panamera
Reliability: Porsche is renowned for its engineering, and the Panamera is no different, offering solid reliability.
Comfort: The Panamera combines sports car performance with luxury sedan comfort, making it a unique option.
Value: While pricey, new, used Panameras can be found at a considerable discount, providing excellent value for a high-performance luxury car.

9. Infiniti Q70
Reliability: Infiniti’s reputation for building reliable vehicles extends to the Q70.
Comfort: The Q70 offers a smooth ride with a well-appointed interior and ample features.
Value: The Q70 often goes unnoticed, which means it can be found at lower prices than more mainstream luxury brands.

10. Cadillac CT6
Reliability: The CT6 offers decent reliability, particularly for later models.
Comfort: Known for its spacious and comfortable cabin, the CT6 provides a smooth and composed ride.
Value: Used CT6 models offer many luxury features for the money, making them a strong value proposition in the luxury segment.

Tips for Buying a Used Luxury Car:
Maintenance Records: Always check the maintenance history to ensure the car has been appropriately cared for.
Inspection: Have a trusted mechanic inspect the car before purchasing to avoid hidden issues.
Ownership Costs: Consider the cost of ownership, including insurance, repairs, and parts, as luxury cars can be more expensive to maintain.

These models represent some of the best options for those seeking a reliable, comfortable, and valuable used luxury car.