I suppose that's up to who you ask. American tier list would tell you Ness is better, supported by the likes of FOW, Yink and, nowadays, Shaky. Japanese tier list would tell you Lucas is much better, supported by the likes of Hyutter and quite a few other top Lucas mains up there (sorry I'm Aus. so Japan is 'up there' for me
).
If you asked me personally, i'd tell you that from my limited experience, they're not far apart and either could be ahead. Ness has a fantastic air game, some great OoS options and a solid grab game. However his tilts are used only in rare situations and his Fsmash and Dsmash are usually just asking for trouble, whereas his Usmash is useful in some situations but doesn't kill for freakin' ages haha. He also finds it so much harder to get back onstage than like 80% of the cast lawl.
On the other hand, Lucas' grab game is not that great, only really useful in some MUs like Oli (kind of) and maybe snake if you're trying to get combos on him at low percents when he's coming down from the air (which unfortunately is illogical because Snake is a ground-based character and shouldn't really be leaving it for many other reasons than he got hit away from it.... =/) and although he has an aerial tether, it actually puts him in a more compromising position than without (when he first tethers he gets hitboxes all throughout the snake ((?)) and just above the snake, he might as well be Pikachu using QAC -_- ) arguably.
He also suffers from laggy smashes which are only really useful for surprise attacks and catching landings and the one that works fast can be predicted (Fsmash) really easily.
HOWEVER, his aerial game is also fantastic (and under-rated IMO, his Fair actually beats Ness' in terms of range even though it has to actually be timed iirc), and he has some legitimate locks and combos. His tilt game is fine IMO with the exception of Utilt which is only really used for that little grab combo at 0-5% and his recovery is actually pretty fantastic, up there with ROB's. His PK fire is more practical than Ness' (although Ness gets a better deal out of a PK fire, he finds it far riskier than Lucas to actually go ahead and use one and if it's PS-ed he's a sitting duck with approximately 20-30 frames of ending lag), going horizontal in the air means he can use it in short hops effectively and finds it easier to time it when both chars are in the air. He can also wavebounce with it, making retreating SH PKFs totally legit and retreating aerially so much fun (PKF ---> Magnet pull is the best AT evar!
).
Both chars suffer from GR shenanigans and
Marth characters that
King Dedede outrange them but in the end I reckon they're both solid mid tiers with the potential to be right next to each other, with places interchangeable.
So yeah, that's my
50 2 cents.