Rio Grande Turtle & Tortoise Club
It depends on what you want and the environment you are able to provide. Box turtles (Terrapene spp.) are very popular in the Albuquerque area due to their relatively low cost and widespread availability along with their ability to thrive with a little help in a well-watered backyard. Russian Tortoises (Testudo horsfieldii) are another popular choice - these tortoises are strictly vegetarian and are adapted to living in somewhat drier conditions than box turtles. Other species are larger and may not hibernate and require more care as a result.
By far the most popular water turtle is the red-eared slider, which baby boomers may remember as those ubiquitous dime store turtles of their childhoods. They are hardy, widely available, and ridiculously inexpensive to purchase; however, those cute little hatchlings and juveniles grow up fast and require a large tank or pond with good filtration to live in.
The most important thing to keep in mind when considering getting a turtle as a pet is that every species has different habitat and dietary requirements, and may be far more difficult to care for properly than what some pet store clerk or roadside vendor may try to tell you.
Do your research before getting any new pet, paying particular attention to any special requirements, adult size, and life span.