I used my first and middle name because I use the saddle on multiple horses and I figured my last name will probably change at some point. If I only used the saddle on a horse I was keeping for the long haul then I would have probably put that horses name on it but however you want to do it is perfectly fine!
My saddles have my first two initials and my last name on them (my name is really long). My saddles are different brands and my grooms know which saddles go on which horse, so it's not a big thing. But I know of barns that have staff that changes a lot or different people at home than are on the road, so they usually have the owner's last name and the horse(s) name that they use on the plate as well. So if you do your own tacking or have a consistent staff, your name would be fine. If not, put your horse(s) name(s) on as well.
Nine out of ten times, you'll get it wrong...but it's that tenth time that you get it right that makes all the difference.
My husband probably hopes my last name will not change, so no problem there. But I have two horses, and my daughter also rides them. I am leaning towards using my name though, but I am curious what most people do.
Mine has my maiden name on it since I've had the name plate (although not the saddle) since before I was married. If I were to get a new nameplate I would just get my first name since it's an uncommon name and my married name isn't very "pretty."
I've seen people with many horses have their nameplates numbered, like "Johnson 1" and "Johnson 2" and so forth. I've really only seen this for pros or pony/junior jocks who ride a lot of horses.
My second saddle has no name plate, but it is a different brand. If I had two saddles of the same brand I would probably number them with my first name.
Last name. We have a few different saddles and it's just easier that way, they're not as much "mine" as they are "my family's." Even if the situation was different I would probably just put my last name, or my first initial and last name.
Opus1, a family friend of mine had a plate on the back of her old western saddle that said "sit down, shut up, and hold on!"
One saddle just has my name and the other saddle has the horse it belongs to me on it and my last name. I bought that saddle specifically for him. As for the rest of the tack, all my bridles and such have the horse's barn name and my last name.
I named my horse "George" when he was a baby (read: long before I met my SO). My SO's last name is George. We've been discussing getting engaged for some time now, and I giggle when I think that after I get married and change my last name, on George's saddle my nameplate can just say "George" and cover all bases. LOL.