a tube, it is not that big of a chore to install a tube on front tires, rear tires can be more of a hassle.
normally the small front tractor tires can be removed and taken to any tire/automotive store that deals with tires, and get a tube installed. rear tires can be a different story.
i prefer tubes in all tires, from filling tires with fluid for ballast, to not having to deal with air leaks between tire and rim, to simply seating the bead back onto rim if i do get a flat. tubes can be some what of a hassle but *shrugs* tubes seem to work better for me. more so when i get a thorn in tire, i can pull tire off, tube out, put some air in tube and with a little soap and water, can pin point leak on tube, and then line things up for good close inspection on tire to find were thorn is.
i use the green goop or what ever it is called, menard carries. wanted for a sale and picked some up. it seems to have worked on some thorns i have picked up already.