If you look to play solo, you should go for Wynn. I'd say that the elf is the strongest, but some people could argue that darkelf is better. You can check their skills on l2wiki and judge. Human is definitely the worst unless they've changed something in the most recent update, that came out recently.
An Iss bot could be useful too. Pre-update PP was by far the best option due to PoM, and cd passive (higher BR uptime). However, they've made quite some changes on Isses as I saw. PP/SwS/BD now have stronger Melodies and OL/WC have stronger sonatas. They're also getting specialized harmonies. If I remember correctly, apart from the typical harmonies, PP gets a stronger knight one, sws a stronger mage one and bd a stronger fighter one. You could check the numbers if you wanna make a better decision.
About server. A friend of mine told me that these two servers, Freya and Naia, are kind of the same deal at the moment and they're probably gonna merge. If so, your decision doesn't matter.