From my puzzle-a-day calendar:
Not superhard, but fun. If you want to spell out the reasoning for your guess, pls. put it in a spoiler box so people coming into the thread after you can play along. Posting more examples of pairs of things he likes and doesn’t like is another way of indicating whether you got the answer or not, and one that doesn’t require spoiler boxes.
He’d like a cab because it has two alphabetically consecutive letters.
Hugh like plaster, spackle and stucco but not cement.
Ahhhh.
Hugh wants plastic, not paper.
Hugh likes bobcats, not lynxes.
Hugh likes death, not life.
Not quite. Close. But not quite.
The same applies to Thudlow’s entries.
Ah, gotcha. Damn (not darn). Hugh likes the OP but not my reply.
Hugh likes suede but not leather.
Hugh likes beef but not pork.
Hugh drinks Nehi but not Fanta.
Yupper – Thudlow has it.
nevermind
Without reading past the OP:
He’d prefer a cab to a taxi. He also likes a blade, but not a knife: a laugh, but not a chuckle; pop, but not soda; Desmond Tutu, but not Nelson Mandela. He’s solemn, but not serious.
Are we open to more of these?
The first one I can remember, when I was introduced to this game is still a classic. Given that we aren’t too much under way, let me toss this near gimmie in.
Apples, but not Bananas
Baseball, but not Cricket
Accounting and Bookkeeping, but not Financing and Investment Banking.
Silver, but not Gray
Purple, but not Indigo
Cooking, but not Baking
Corvette, but not Mustang
Rabbit and Bunny, but not Hare
As for
would it be correct to add:
Orange, but not Pumpkin?
Baccarat, but not Chemin de Fer.
Yes. Indeed. Not sure what else you could add, ater that though.
Yep.
Okay, I’m totally not getting this one – could someone spoilerbox an answer, pls?
Without looking at others’ answers, my first thought is that he might like a taxi and a cab, but it seems unlikely to be the answer. Let me try:
Does he like an auto but not a manual?
ETA: having looked through the thread, pretty sure I haven’t got it. This is going to be a “kick yourself” moment, I’m sure :).
The words silver, purple, and orange don’t have any “real” rhymes in the English language.
Ah, gotcha. Thanks.
And Dead Cat – nope, whatever you’re thinking, it’s not right. 
Okay, here’s a hint:
He liked Blade but not Matrix; he gets high but not stoned; he will stop but not cease.