Any standard size servo, or low profile servo can work.
I personally use a Xpert 4000LV servo in my 4wd associated, its 90 bucks, pretty speedy and torquey, but is a bit outdated and can only max out at 6.6v.
Cheapo Amazon ones, metal gear, aluminum case, 20kg to 45kg should be just enough for a buggy. Even better if it's HV compatible so you can get more speed / torque if need be, but note your receiver and other things plugged into your receiver has to be HV compatible too.
Do you know if this losi is a 2wd or 4wd?
Also most servos these days use a 25T spline and a TLR 22 - 25T aluminum horn should be a direct fit with the car. I use that servo horn on 3 of my cars and it holds up well.
Most of the club racers and higher level drivers use servos like protek, tekin, xpert, nitropro, Futaba, hitec, savox. Those are the main brands but there are several more out there.
@Littlemotor is the NitroPro nerd on here lol
But they are top of the line expensive though
Oh yea, Ecopower is also a decent servo brand aswell. Mostly used as cheap RTR replacement servos for bashers but can work in a buggy