unless you're going to lay down all your other instruments and play nothing but fretless for the next six months I would recommend you go with a fretted neck
fretless bass is an entirely different animal than a fretted bass. you don't simply play fretted bass without the frets when you go fretless. you need to develop muscle memory by continued, frequent, regular, precise repitition. it's not an instrument you take casually if you want to play it well. and you also need to develop your ear so you can hear when you're in/out of tune by 1/64" of finger placement or so.
a fretted bass will serve you well for the occasional weekend fill-in gig when you're really a guitarist at heart. a fretless bass will get you a weekend to drink beer -alone- when you're really a guitarist at heart and you haven't put forth the disciplined effort to become proficient
so ... can you precisely hear pitch and find fault with cheap electronic tuners? are you willing to devote yourself to nothing but fretless for the next 6+ months? are you willing to practice precisely to build muscle memory for your finger placement? will you be OK three months from now when you still totally suck? (at fretless playing, of course :laughing7
if you answer no to one or more of these questions, you really need to go the fretted route and save the fretless for when you're truly ready to give it your undivided focus
fwiw I've played 4, 5, and 6-string fretless for years and I don't need no stinkin' lines, but having not played much the past two years I wouldn't even consider playing fretless with others unless I wanted to guarantee that I never had opportunity to play with them again anytime soon.
all the best,
R