"Croom A and B" are the trails that I've repeatedly hiked and biked in Withlacootchie. To get there, park at the Tucker Hill Fire Tower and enter the trail from the parking lot. The area is not mapped out well, so bring a compass and a GPS if you have one. Your cell phone will not be of much use since there is weak or no signal. From what I've been reading recently, the map and blazes are now better marked, but i would not bet on it.
Despite the negatives, Croom is a great place to hike and bike. The trails are hard packed and most of them stay dry even during the rainy seasons (stay away from the lower elevation on the east side near the lake). Croom's real gems are its hidden features: an abandoned open-pit mine (or who knows, maybe more than one), and an abandoned cemetery (located near the start of the trail loop on one of the trail offshoots to the right). Neither is marked on the map.
Croom's hiking/biking trails venture mainly through higher elevation scrub land, so it tends to get hot in the summer time. I stick to hiking these trails during cooler weather. The scenery is fantastic, some of the best I've seen, and apparently, some of the best in the US according to other hikers. Also, there are a lot of different areas to Withlacootchie, Croom is just one of many with different ecosystems. If you prefer an area that's a bit more wet or lower elevation, Withlacootchie's got that, too.
Not my favorite place to bike, but it's a great workout. Put on some good tires and bring plenty to drink. The majority of the trail is packed sand/dirt/leaves, but the loose sand areas will certainly slow you down if you don't have decent tires.
There's also a 12 mile loop if you don't have as much time / energy.