Ok, its a really common question and you are in the correct place for loads of good advice from racers
These are my own very very humble opinions:
2wd - you can't go far wrong with a good nick Associated B4/B4.1 really. Super easy to work on, loads of spares available, and tonnes of driver support due to the platform being ever populer. Fairly simple base set-ups and importantly a forgiving and visceral car to drive.
4wd- the Associated B44/B44.1 is a solid and reliable buggy and is often quoted as being a dream to drive for new hands in 4wd. Again,spares are fairly easy to obtain and the cars are nice to work on.
You can pick up either for a good price here on oOples trader section and watch out for a Factory Team version as you will be pretty much 'race equiped' with all the solid stuff (titanium turnbuckles etc)
There really are so many opinions (all very valid) and sooo much choice out there for 1/10 these days. Most of us will give the same advice when you make the jump in buying your first buggys, go with a brand that has proven products, solid spares back up (you will break stuff as you are learning, in fact we all do) and easy to set up and drive. Most of us have owned one or both of these Associated cars or at least one of the modified versions of these platforms over the years.
Most experienced buggy owners will agree, buy a common buggy at first, learn how to strip it totally and rebuild every part. Race it and ask as many questions as you can from your fellow racers, most of all have fun