Not so fast. I have heard differing opinions on which is better and after doing a lot of research, I am leaning towards bolt-on rather than wend-on sliders for a few different reasons.
1) Some well respected rock slider manufactures use bolt-on installation rather than weld-on. These sliders ain't just for looks.....
Rockrails, rock sliders, rocker protection
4th Gen Toyota 4Runner Rock Sliders, Toyota Rock Sliders, ShrockWorks
2) If you ever want to take off the sliders, or change brands, or (heaven forbid) you get in a bad car accident that requires frame work, weld-on sliders can get int he way. Whereas bolt-on sliders can simply be removed. No cutting or plasma cutters required to pull of bolt-on sliders.
3) You can install bolt-on sliders yourself, saving you significant $$$ from having to pay someone to install them for you. I've heard a couple of jack stands and a buddy will definitely help, but you can probably do a bolt-on slider install yourself within a couple of hours and without the need for welding gear and welding ability.
4) I went to Slee Offroad to ask them about sliders for my 4R. They are very well respected in the Toyota, specifically Land Cruiser, communities. I asked them about sliders for my 4th gen and they said they don't make sliders for 4th gen 4Runners. They said they would be happy to install any sliders that I bought and brought in, but they recommended bolt-on vs. weld-on. This is coming from a company that specializes in custom fabrication work, so welding is not a problem for them. I didn't get into the specifics as to why, but I certainly respect their opinion. Again, it's not gospel, but it was coming from some people that I trust and have done work on my 4Runner in the past.
I'm not saying weld-on sliders are bad, but I wouldn't be too quick to dismiss bolt-on sliders, either. I'd be curious to hear other opinions of people that are running sliders currently.