A while back I was playing a 2 handed Summoner, I focused on using a 2 handed weapon with the Eidolon.
I had the souldbound archetype and was playing a Half Elf with the fcb so my evolution points where beyond the norm. This also meant by Eidolon could take evolutions it doesn't meet the sub type requirements for.
What would be the best attack set up at around level 15, some combination of weapons and natural attacks or just natural attacks?
Not too sure on most of this, but general conventional wisdom, is that you do NOT want to mix weapon attacks with natural attacks. When using weapons, all of your natural attacks convert to secondary, and the accuracy penalty is makes them less worthwhile. If you plan on using your eidolon to ginsue through mostly low ac minions and mooks, the plethora of attacks might work for you. But from a feat, enchantments, and other resources perspective, it's usually better to focus on one or the other. I like animal types and natural attacks, but I'm pretty sure the weapon wielding eidolons are the ones topping out the dps meters.
At 9th level, the eidolon gets multiattack for free, so the secondary natural weapons are only at a -2 penatly. Not great, but not out of the question to combine weapons and natural weapons at level 15.
I was thinking claws may be the best option because of rend but then you can only have 4 until level 14 so you'll probably only proc it once per full attack.
So weapon and secondary's may be the best option once haste becomes available.
Edit: but then haste would give you an extra chance to proc rend