dude the second build is better because of simple fact called rank 8:
with rank 8 dragon2 already get the attribute for 100% extra damage and dethrone.
where hoplite2 you would get more finestra and spear lunge (but since sepertine is better, it does not count).
now:
i must say that a mounted tank is far more fun to play than a normal tank, i myself have a sw3 cata dragon and a sw-petalhopcata where i wanted to play as tank, my last round of pvps was even with him, but back on topic.
now with rank8 so close; going with dragon is better because let’s remember that for tanking you also need to dish out damage and for that dethrone will be a must.
now on the aspect of tanking in general i must also advice you that the era of mounted tank(spear+shield for tank) is almost over, simple because of the fact that some of the new onehand swords have up to 300-400 defm bonus (check the ktos thread and the post from last maintenance 2 weeks ago for details) , and this is a huge defm bonus for tanking, and of course nuela cards, nuela cards bost Mdef by % and together with those swords you can achieve a fair huge number of defm, allowing for a 1hand-shield con-dex swordsman tank Mdamage and Pdamege with evasion, this is it about mounted tank, is not impossible to do but like i have wrote with 1handsword shield built it will be fair more easy.
now on the second aspect of the class, if you are going for tanking being full CON with low str is never the answer in fact is wrong , again for tanking in this game you need to dish out damage as well, is not press C and wait, this is nuub way to tank and no one will take you serious as tank if you only do that.
so the stats for a good tank is CON_DEX, going up 1-1 is good, or more dex if you like, since once you reach 30k hp that is fair easy to do, is already enough to tank most of the contents in the damage and dex is already obvious is to allow you to tank Pdamage with evasion and the con the Mdamage.
Now i will write a little of why the era of mounted tanks is almost over, and the simple reason is because the build with petel-rodel-shinobi murmilio can not only tank better than the mounted tank, but also dish out a fair better damage as well (the built with dragon that is better as damage dealer is hop3-doppeldragon not the catadragon) so the only benefit that a mounted tank was over murmilio comes with dragon2 and that is serpentine buff, that would allow us as tank to boost the melee damage of our party members as well, allowing for huge bursts of damage, and this is in fact the only advantage that a mounted tank have over the murmilio version, and for that you need dragon2.
this is it, i hope that is useful if you have more questions feel free to ask, but as last advice i must say that if you are in search of mounted tank i believe would be better for you to remove the desire to be a full tank because it can not be done right now, because as mounted tank we simple lack the tools to effective tank Mdamage but even them is possible to built a mounted-off tank, where you can not only tank when necessary but also help is other areas as well, and this is the place that a cata-dragon should follow if she or he desires to be a one hand spear-shield user.
On a side note, just now i saw that the people have resurrection this topic from 5 months later and and i do not even think you are playing anymore, but i won’t erase my walltext i will just post this here because it may help others who have click in the topic.