Rebirths are just a lazy way of making players continue playing your server. (Unless there's a real meaning to it, such as DeathzOt's)
Max level isn't very good either, since it creates a limit and you must balance around that limit, and as you increase the limit (which you will), it will upset the balance of previous things as well as future things. An example would be like most WoW-esque MMOs. At first the cap was 60, and it was tough doing dungeons and gear with around 150 damage was considered godly.
Now, the cap is 110. All the content that was previously difficult is now not, and on top of that, monsters that are normal crappy tier but level 100 are going to be MUCH MUCH MUCH MUCH MUCH harder than level 60 badass animated/art monsters. Also, weapons are known to have around 2K damage now.
This might seem okay, but it causes a problem for people not currently involved in the game itself. If you played WoW during the all the expansions, you would progress with enough time (if you played everyday) that your gear would be maxed and you'd wait for something new to come along, as well as completing all the dungeons and what not.
But the player who just joined will most likely skip all the major dungeons that were difficult at the time, up until the new cap of 110. Even Blizzard realizes this and now sells max level boosts to 100 and let the player play the latest expansion as intended.
EDIT:
I might be biased but I think Tibia's system is still my favorite to date. It allowed players to experience anything in the world, meaning real unfairness at times. This along with experience loss, item loss, and supply cost made for a system that made it feel like levels were important, but so was being prepared/safe.
It also allowed players to challenge themselves. I remember I tried nonstop as a level 30 paladin to solo a lured Giant Spider on my way to Dark Cathedral, only to have it kill me 90% of the time.