I have two wheels in front. This is called a tadpole trike. Eight gears is fine, on a flat and smooth surface I am going about 11 miles an hour when my pedals are spinning freely with no resistance. I’m sure I could go faster with more gears. But with more speed comes more risk of tipping. I use my brakes on downhills because I get scared. My bike is wonderful on paved trails and streets. However, I rode on crushed stone trail last weekend and it was hard. I imagine a person with better leg strength wouldn’t have a problem.
A trike with 2 wheels in back is called a delta. I don’t have any experience with these.
if you can get somewhere to try some out, you can narrow your search considerable. Factors to consider besides delta vs tadpole would be seat height (for getting in and out), type of shifter (derailer vs internal hub...love my internal hub), price (of course), How easy or hard it is to get parts for repairs (don’t recommend something obscure or overseas even), Type of pedals (this can be a big deal, you should find something that will keep your foot on the pedal so when you get tired your foot doesn’t fall and get caught up under your trike. Many people use the click-in type where you have to have a special shoe to fit the pedal. I use power strips that is basically just a strap over the top of my foot as I prefer to wear my sandals), also consider if you will be needing to transport your trike and if it will fit in your vehicle, although most fit in small suv, have seen some in a hatchback and also have seen some on a shelf hitch thingie.
Thats the basics, I’m sure I’ve missed something. But the more you learn about the different choices, the easier it will be to sort it all out. Safety, Fit and function are primary.
It will cost you a bit as these are expensive. If that is a concern, start taking a look at Craig’s list and Facebook marketplace. I found mine that way. It had been ridden a grand total of 3 times by an old man who grandson bought it for him. Then was stored in a garage for 3 years. Lol. It was perfect.
sorry for the novel. I love my trike and am excited for you to be considering one. You won’t regret it.