First time to Belize and wanted to visit a Mayan Ruin while there...which do you suggest? Also, how would I get from Placentia to Tikal without going back through Belize City?

I went to Altun Ha, was perfectly content with the ruins there. I didn't go to the others so I can't really say that Altun Ha was the best.

Of the ruins easily accessible from AC I find Lamanai more impressive than Altun Ha.

Lamanai!

Having visited most of the major ruins in BZ,as well as some of the smaller, I vote to make 3 in a row - Lamanai, and book Daniel Nunez, Tanisha Tours. The man is unbeatable! Assuming of course, you are considering a daytrip from SP.

Lamanai hands down for your first visit. I agree, Daniel Nunez was excellent.!

Lamanai with Daniel Nunez!

Lamanai! it's so beautiful! but it's a long boat/bus/boat ride... but so worth the trip!!!!

Lamanai, even the long boat ride is a great nature trip. Tourist ask me about Birding tours every day. I tell them 'Lamanai' for pristine canopied rain forest habitat, you also pass thru mangrove river habitat and riverine habitat. Best ruins and artifacts on display. There are half a dozen operators in San Pedro that do the trip and all seem to do the same basic Lamanai trip.I couldn't say one guide was better than the other and I've done the trip with them all at one time or another in my 20 years of birding by boat.
Tikal is a pain in the butt to get to and no better than Lamanai

Xunantunich is amazing!!! This is in the Cayo district. If you climb to the very top you can see Guatemala!!