There are only 2 clients that work with EQEmu right now; Titanium or Secrets of Faydwer. LDoN will definitely not work.
Titanium is hard to find, but you can also use Secrets of Faydwer on the servers that run the current code. SoF is almost caught up with Titanium as far as EQEmu compatibility goes and soon it should be fully caught up. Might as well get the newer client unless you are planning to play on a server that doesn't update and doesn't support SoF yet.
Note: You can get SoF from
www.newegg.com for $4.99 with free shipping right now. That deal is nearly impossible to beat. It is probably $500+ worth of expansions if you bought them all separately when they first came out (which I bought double of most of them since I 2 boxed on Live), so $5 is a steal!