Folks who are fortunate enough to own a sports car for some weekend apex-clipping know that, above all else, a sports car is something to be treasured. Most owners keep their pride and joy under wraps – or under a car cover – in the garage until the time is right, the sun is shining, and the temperature is warm enough to allow for some open-topped driving. However, when it comes to sports car reliability, some are much more well-equipped in this regard than others.Take the Mazda MX-5 Miata. It's regarded as one of, if not the most reliable sports cars money can buy, and its usual market price is rather agreeable. But, what happens if you don't want to go with the grain, and want some other kind of reliable sports car?That's where the BMW Z4 comes in, specifically the 2019 model year. When compared to the MX-5, it's not too far away in the reliability charts, and the premium you pay for its BMW badge isn't all that hard to swallow, especially when you learn just what the model has to offer.This write-up pertains to the 2019 BMW Z4 sDrive30i, as it was the sole iteration offered for the fifth-gen Z4 in the US market. A Bargain Bimmer Sports Car BMW The fifth-gen BMW Z4, also known as the G29, first entered the US market in late 2018 as a 2019 model year. While there are three trim levels that come with the G29 Z4, it only offered the "sDrive30i" grade during its debut year. Upon its US introduction, it stickered for just about $49,700 before any destination fees or miscellaneous taxes were factored in. Its Mazda-bred competitor, the MX-5 Miata, on the other hand, sported an MSRP of just $25,730, nearly half the price.BMW However, things are quite a lot different when it comes to pricing these days. According to our Pricing Trends analysis, the '19 BMW Z4 boasts an average used market price of just $29,037, roughly $20k cheaper than it was when new. If we get technical and factor inflation into the equation, its original MSRP of $49,700 was actually around $62,632 in today's money, meaning its current real dollar value is roughly $33k less than it was when new.On the other hand, the 2019 Mazda MX-5 Miata boasts a current average used price of $19,854. Of course, being from a non-luxury, Japanese brand, coupled with its penchant for superb reliability, means the Miata holds onto its value extremely well.BMW The 2019 Mazda Miata wasn't the Z4's only competitor that year, just one of its more direct ones hailing from the more-mainstream market. In reality, the model was destined to battle it out with other nameplates like the Porsche 718 Cayman, the Jaguar F-Type, and the Mercedes-Benz SLC-Class. In the table below, we'll flesh out all of their current values, alongside the Z4's, and see just how much of a bargain the Z4 turns out to be. We'll also include original sticker prices and a value percentage to make things interesting: Just How Reliable Is It? BMWUnfortunately, the 2019 BMW Z4 has its work cut out for it when it comes to proving its reliability. If we just pop over to RepairPal.com and search the model, we're greeted with a 14th-out-of-17 ranking among luxury compact cars alongside an average annual repair cost of approximately $895 per year. Most reliability-rating sites are along these lines. However, if we turn our attention to Kelley Blue Book's consumer reviews section for the model, its reliability is rated at 4.8 out of five stars, a much better mark.When it comes to the 2019 Mazda MX-5 Miata, RepairPal.com favors it much more than the BMW. Its reliability ranking is set at eighth out of 21 subcompact cars ranked by the site. In addition, its estimated annual repair cost is just $421 per year, less than half of the BMW's. In short, the rather poor ratings from RepairPal.com mar the Z4's reputation a bit. The good news is, however, that there are two key aspects of the G29 Z4 making up for the bad grades in spades.BMW The first important part is its engine. It's a 2.0-liter, twin-scroll-turbocharged inline-four-cylinder engine. The mill's technical name is the B48, which is its own engine family in and of itself. Its construction is notably robust, featuring things like a closed-deck block, meaning its cylinders and cylinder head mating surface are reinforced, much like a purpose-built racing engine. It also packs forged connecting rods and a forged crankshaft. It's undersquare in design, meaning its piston stroke is longer than its cylinder bores are wide. Undersquare engines typically produce more torque at the expense of higher revs, and those who are mechanically inclined will know that an engine that spins slower is, usually, less stressed.BMW The second piece of the 2019 Z4's reliability pie is its transmission. It's an eight-speed automatic unit produced by the German-based gearbox-maker ZF Friedrichshafen AG, or "ZF" for short. It's designed to be sporty for the Z4 application, taking advantage of shorter gear ratios in lower gears to help facilitate quick acceleration.However, higher gears are wider to maximize highway efficiency. Its torque converter is also built to last, as it takes advantage of things like a Twin-Torsional Damper (TTD), which helps to reduce in-car vibrations and ease physical strain on the transmission itself. How The 2019 BMW Z4 Actually Compares To The Miata 2019 BMW Z4 Of course, you can't really compare the Z4 with the MX-5 Miata in a direct, apples-to-apples manner. The Mazda is firmly within a lower rung of the automotive market, and is much more aimed at the mass market. The BMW, on the other hand, belongs in a higher class, and offers more style, refinement, and a larger standard features list than the MX-5. The Bimmer also makes a decent chunk more power, with its 255 ponies versus the Miata's 181.BMW However, we can compare value for money and reliability. The BMW manages to retain 57.4 percent of its original value, more than most of its competitors we showed previously. Of course, the Miata beats it by miles when it comes to value for money, but for a luxury roadster, the Z4 does pretty well. Its reliability isn't that great when viewed on a majority of review sites, but Kelley Blue Book's consumer reviews are much more favorable, and its use of the B48 engine and bulletproof ZF transmission mean it's set up for the long haul.BMW In the end, though, if you just want a good little sports car that gets the job done without much fuss, go with the Mazda. But, if you want a little bit more pizzazz and "head-turnability" from your roadster, the Bimmer is a great choice.