I don't like the rule of "oh you took a long rest, your health is full." it doesn't make sense and it just allows the party to fully heal whenever they want as long as they are in a safe area. what do you use instead of max health?

Few things.

You can only benefit from one long rest per 24 hours (really 16 hours after the end of one long rest before they can begin another). So the party can't just rest whenever they want to heal up. Once per day.

Second, the DM (you?) is the arbiter on whether or not the party can rest. They can sit around for 8 hours but you decide if they get the actual long-rest benefits.

Third, the party isn't immune to being attacked while resting. If somehow they're doing it too often (although once per day probably isn't too often), you can drop a random encounter on them.

Regarding healing, it helps me visualize HP recovery not as healing in a Wolverine sense, but just a general restoration of fighting fitness. You take a stab wound of 6 HP, then rest. The 6 HP are restored, sure, but you still have the stab wound. Maybe it's closed up a bit and not really bleeding any more, but it's still there. It's just no longer a concern when it comes to surviving a fight. HP isn't literally health -- it's a measure of how well you'd survive a fight. People can fight with injuries, especially older ones that aren't shocking their systems or causing weird systemic/metabolic effects.

I'm talking about rest-based HP recovery here. A casting of cure wounds is likely actually healing up the injury. But in the end, mechanically, it doesn't matter either way.

I agree with the idea that someone who was literally stabilized from dying 8 hours ago could be back to full right now and not suffer any ill consequences (as an extreme example) is patently absurd and wildly unrealistic.

However, the D&D game and everything about it is balanced on the assumption that after a long rest, the characters are "back up to full". If you prevent that, then you're going to have to rebalance everything you do to account for it. Not impossible, but something you have to be aware of.

You could try using the "Gritty Realism" option, of the Short Rest taking 8 hours (and can only be done 1/day) and Long Rest taking a week (so you'd need to go back to town to do it or something).  But when you do this, you need to rescale all your encounters. And you need to expect short dungeon excursions and lots of downtime in town. The book recommends this for City adventures, political intrigue, etc.  But you could do it for dungeons. Just be aware of what this does to the game balance.

Encounters in published adventures are based around the party being at full resources (HP, spell slots, etc).

The best thing I can suggest is to have more than one encounter per day.

Quote from crispybits2004 >>

I don't like the rule of "oh you took a long rest, your health is full." it doesn't make sense and it just allows the party to fully heal whenever they want as long as they are in a safe area. what do you use instead of max health?

 Its been around since the dawn of time.  If they stay over night they should be at full health.  Now if they abuse it by staying in a dungeon for a long rest just throw in some encounters to remind them no meta gaming.  And its not really an issue to "prevent", just adjust your encounter strength accordingly.

Quote from EggKookoo >>

Regarding healing, it helps me visualize HP recovery not as healing in a Wolverine sense, but just a general restoration of fighting fitness. You take a stab wound of 6 HP, then rest. The 6 HP are restored, sure, but you still have the stab wound. Maybe it's closed up a bit and not really bleeding any more, but it's still there. It's just no longer a concern when it comes to surviving a fight. HP isn't literally health -- it's a measure of how well you'd survive a fight. People can fight with injuries, especially older ones that aren't shocking their systems or causing weird systemic/metabolic effects.

 This sort of healing logic works within the abstraction the game system creates.  The "wounds" that a player takes right up until - at times - the very last HP the character has is not a real wound.  It is a measure of fighting fitness and their ability to perform tasks.  In 1st & 2nd edition our group's games had it where the first Hit Die you had was real dangerous wounds.  Everything after that was because you were a HERO!  We just had it where you healed the 2nd and higher HD's HP faster.

It was an attempt to make it a little more gritty.  The 1st level hurt real bad and took us forever to get to 2nd, but it was interesting the 1st time we did it.  The second was annoying and I think we got rid of the system before the 3rd campaign.

Quote from BioWizard >>

 

You could try using the "Gritty Realism" option, of the Short Rest taking 8 hours (and can only be done 1/day) and Long Rest taking a week (so you'd need to go back to town to do it or something).  But when you do this, you need to rescale all your encounters. And you need to expect short dungeon excursions and lots of downtime in town. The book recommends this for City adventures, political intrigue, etc.  But you could do it for dungeons. Just be aware of what this does to the game balance.

 I use this in my games.  It also has the side effect of players becoming more tactical and resorting to things other than violence if possible.  I rescale my encounters a little, but not much at all.  I have even had long dungeon excursions where the party was in the Underdark for months, and parts of the world changed while they were gone because of it.  It does very much knock the game off balance, but if you're planning for it, it isn't that bad.  Nefarious plots from the bad guys take longer to develop too because of it.  It also makes characters with short rest recovery abilities more powerful, while full casters and characters who have more long rest recovery abilities less powerful.

All in all, I was tired of the "sleep off the major wounds" trope, and I'll never turn back.

 It does very much knock the game off balance, but if you're planning for it, it isn't that bad.  

That's the main thing -- you have to plan for it. You can't use "gritty realism" and then try to do something like run a published module as-is. It's written assuming a full heal-up every (roughly) 24 hours... if you don't allow that, then you have to debuff the encounters or spread them out or something.

Quote from BioWizard >>

I agree with the idea that someone who was literally stabilized from dying 8 hours ago could be back to full right now and not suffer any ill consequences (as an extreme example) is patently absurd and wildly unrealistic.

 I mean so is creating a fireball from nothing or taking less damage from falling off a cliff because you're angry. If you want gritty realism you're playing the wrong game.

Say the bedrolls are enchanted or the god of dreams heals you or whatever. It's no less plausible than 75% of the things that happen in this game.