Of my two favorites, I went with the Eureka Zeus 1Exo tent instead of the Sierra Designs Light Year.

Reasons:

The Eureka is Free Standing and easy to set up.  I had a really bad experience with solo tents and rain once because I couldn't stake it out tight enough.  The clips vs. the sleaves for tent poles looks like a MUCH more convenient way to set up.  I have bad memories of pole sleaves as well. 

The Eureka has a bigger vestibule.  I want to be able to stash my pack and my boots in the vestibule so as to have more room in the tent proper (particually if I'm stuck in there due to a storm).  I have only seen one review out of countless others that said the SD LY had a big enough vestibule for this 

The Eureka is actually a few ounces lighter than the SD LY as well.  Not a huge factor, but I DO want to carve a few pounds from my base weight where possible.

Disadvantages:

The Eureka may not vent as well.  This I am prepared to live with.  I really don't think either tent it going to vent 100% anyways.  That's one reason I am going with a synthetic bag vs. a down one. 

The Eureka is single walled.  This means that the tent may come under a bit more wear than the SD LY.  This prospect I am prepared to live with--I will make sure to have adequate repair materials in my pack. 

The tent fabric feels a bit thin to me.  Bear in mind I haven't actually compared it face to face with other tents so they might ALL be like this...this is where I hit a bad spot by not having an outdoors store to go too...I am getting a ground cloth, despite the extra weight it will cause.

The seams are not as "bathtub" as I would like.  I certainly hope this won't cause a problem.

I'm unsure whether my pack will fit in the vestibule...The zeus has one of the largest vestibule square footage's of many solo tents I've researched though, so I think this is a common problem.  This is something I will work out once my pack is delivered (any day now hopefully...)
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On Tents vs. Tarps:

Bottom Line: 

Comfort.  I don't mind carrying an extra pound or two to be safe and curled up in a tent vs. an open air tarp.  I prefer the protection from bugs.  I like the idea of being able to actually live in the tent (as opposed to a bivy shelter) during a zero day if so desired...being able to read, to write, etc. 

On clear nights I may decide to not pitch the tent and stargaze.  This is another reason I am not getting a Down filled sleeping bag.  However...I still want the option to decide when and where!