Antenna discussions in the ADSB aircraft tracking world generally devolve into firestorms of opinion! Nonetheless, improving antenna performance will usually have a significant effect.
This paragraph considers only omnidirectional vertically polarized antenna systems; directional antennas are discussed elsewhere.
The simplest way to evaluate possible changes is to consider only the technology of the antenna. Generally (but not always), price correlates to performance. Sometimes, it is possible to make your own antenna, but that is beyond the scope of this post. You should consider a better antenna if your initial setup uses one of the lower-performing technologies.
As with every suggested enhancement, be sure to do the before and after tests and carefully review the results. There are four general technologies offered in the hobbyist marketplace, and many vendors exist in each technology.
The technologies are, in general order of increasing performance:
i. A wire. Some users say a straightened paper clip will work! That is true, but a correctly cut and mounted quarter wave vertical dipole will have better performance and definitely better reliability. Something like https://www.amazon.com/Bingfu-100MHz-1800MHz-Magnetic-Compatible-Software/dp/B07HQJKMBD/ represents the type of system. These antennas should be used only indoors, unless specifically rated for outdoor use.
ii. A printed circuit board antenna. Fairly inexpensive printed circuit boards that act as an antenna are available. Unless encased, they should be used only indoors. An example is at https://www.amazon.com/Acxico-1Pcs-ADS-B-1090MHZ-Antenna/dp/B083XQY2ZP/.
iii. A rubber ducky antenna. https://www.amazon.com/NooElec-ADS-B-Discovery-Antenna-Bundle/dp/B01J9DH9U2/ shows an example. Generally, these antennas are good for portable or initial use, but will not survive long outdoors.
iv. A co-linear coaxial antenna. Known as a CoCo, these antennas are probably the most widespread and cost-effective in the ADSB hobbyist world. You can make your own, but the commercially produced versions are sufficiently inexpensive to make construction unattractive for most persons. Many are suitable for outside use, though beware of low-cost antennas that have permanently connected cable pigtails. You want an antenna that has a true outside-rated connector such as a Type N permanently mounted at the base of the antenna.
An example is at https://www.amazon.com/1090MHz-Antenna-Fiberglass-SMA-Male-Extension/dp/B09BQ4H26L/.
High performance, high quality antenna systems are available, right up into the very expensive realm of commercial systems. They exist for both indoor and outdoor antennas. Generally, in this hobbyist arena, it is not effective to look at the top-end commercial systems, other than as systems to drool over. Usually a better hobbyist antenna is most effective if mounted outside and as high as possible, as described elsewhere.
Some examples are appropriate.
An example of a high-quality indoor antenna is https://dpdproductions.com/collections/aviation-base-mobile-antennas/products/ads-b-blade-indoor-antenna?variant=15998161551418.
An example of a high-quality outdoor antenna is https://dpdproductions.com/collections/aviation-base-mobile-antennas/products/ads-b-vertical-outdoor-base-antenna or alternatively https://vinnant.sk/store/product/cc10909-pse.
For Europeans:
https://webshop.jetvision.de/en/product/a3-ads-b-antenna-1090-mhz-bundle/
Also, for the USA and EU Aircraft Band (118-136, 1090Mhz) : Sirio Antenna, High Performance Antenna Made in Italy They have a warehouse in the SF Bay area, and shipping is cheap because of the reduced length of the airband antennas compared to the DPD antennas. I have the one at the top of the list for ACARS and VDL2.