After searching over and over again and again, I need a definite answer to which one will be best for efficiency and not need to be replaced after a few years. My architect wants to use eifs, I like the fact that it adds alot of r value over the exterior of the home but the problems associated with it and will we be able to sell later on. The hard coat stucco over 3/4 blue board came up online and said to staple foam board over osb then 2 layers of paper and nail the metal lath up and stucco. Any input would be appreciated.

Don't consider either without an air gap to promote drying. Maybe with StuccoWrap.

EIFS is cheaper, but more prone to problems and thus less sustainable. From an energy efficiency point of view they are the same.

XPS (blue board) is fairly vapor retardent, (about 1.5-1.8 perms @ 3/4") and in combination with StuccoWrap would be enough to protect the OSB from high vapor drives, provided you have at least 1/4" of air gap between the wire-lath and the wrap.

As manufactured in the US, XPS isn't very green, since it's blown with HFC134a, which has a global warming potential ~1400x CO2.  As the HFCs bleed out over the next 25-50 years doing it's damage, the R-value of the foam falls too, eventually settling to the same R-value of EPS of equal density. EPS is blown with pentane (only 7x CO2 GWP), and has a stable R-value over time.  

Local climate matters too.  If you are putting foam on the exterior of OSB sheathing it's important to keep the average wintertime temp of the OSB above the dew point of the interior conditioned space air or it can load up on moisture, developing mold/rot from interior moisture drives.  With EIFS applied directly to the foam drying toward the exterior is effectively blocked, making the dew point control aspect even MORE critical.  IRC Chapter 7 spells out minimums for the exterior R, specified by US climate zone, but those are minimums- it's worth going higher, especially if going with vapor-tight EIFS, or hard coat stucco (even with the ventilated gap), to keep the OSB warmer (=drier) no matter what, and leave the interior side fairly vapor open (latex paint finishes only, and no vapor retarders unless it's a "smart" vapor retarder such as Intello Plus or Certainteed MemBrain.)  While 3/4" XPS (R3.75) might meet IRC code min for purposes of chapter 7, under EIFS  or hard-coat stucco you'd want R6 or better.

Note also, the IRC prescriptions in Chapter 7  presume R13 cavity insulation for 2x4 framing, R20 for 2x6. The higher-R the cavity fill, the more exterior-R you need for dew-point control. In climate zone 4 can't just stick R3.75 foam on the exterior of a double-studwall or other high-R assembly without an interior side vapor retarder- it has to maintain the same foam-R to cavity-R ratio.

If yours is indeed a 2x6 framed wall, you'll be much better off dropping the framing to 2x4, and bumping the foam up to 2" or 2.5" EPS.  It will have about the same or slightly better "whole-wall" R as R3.75 on the exterior of an R20 2x6 assembly, but FAR better moisture resilience.  With 2" of EPS an 1x4 furring for maintaining the ventilation gap between the hard stucco & metal lath, the wall thickness would be about the same as EIFS directly applied to 3/4" XPS.

Ok, I will talk with my architect and let him know. He was planning on going 2x6 framing. This is being built in cypress texas, nw of houston.

Dana1 - That article you been posting: "High R-Value Enclosures...etc.." I read the whole thing, that stuff blew my mind. Thanks for the source!!

That's Buiding Science Corp.'s  ba-1005 piece, I assume? 

It's not a bad overview- recommended reading for anyone shooting for "better than code-min". 

At ~60 pages it's a pretty good bedtime story too!

This may sound a bit off subject. What about aac sandwich panels. I read somewhere that a guy made his own hybrid panels using 2" aac, 3" foam, then 3" aac. He had 8"×8" reinforced concrete piers every 12 feet. Said the house at 5000sq/ft cost less to heat/cool than his last house at 3000sq/ft that used spray foam and foam sheathing.

Dana1 - Yep that was the Building Science Corp's. So I went and read their High-R value for Roofts article as well. Good bedtime story for sure. I'm just trying to catch up on the learning so I can read posts & understand them.

Ok, our plan of attack, 2x6 framing on 16" center's. No osb except in corners and other openings. 2 layers of 1" foam staggered to create an air tight envelope. 3 coat traditional stucco. Our stucco contractor said he's going to use 3 layers of paper, "whatever that black paper is called" and some special screws. Said this is real common in Austin. Windows will be outies on built frames. Any suggestions I should bring to the stucco guy let me know. I did ask about how solid it will feel and he replied more than over osb.

what sort of windows, I mean do they have a fin and integrated J-channels, or something other?

Unsure of what windows we are using. We haven't broke ground yet. Just getting the construction plans finalized. Any suggestions on what kind?

Regarding your rigid foam insulation, since you are located in a hot climate, I would consider using something like Atlas Rboard - a rigid polyiso insulation with fiberglass facers. Very durable with high R value (~R6/inch). Since you are installing 2 layers of 1" rigid foam in the field of the wall, I would install 1/2" then 1" foam over the OSB in the corners to bring everything out flush.

Here is a link to the Atlas Rboard specs:

http://www.atlasroofing.com/continuous-wall-insulation/rboard

This material is commonly available here in Arkansas at most lumber yards (I've never seen it at a Home Depot or Lowes).  And the cost is about the same or sometimes slightly less than XPS blue/pink board at R5/inch.

Regarding windows, were you planning on wood, vinyl, fiberglass, or what type of frames?

Being in a hot climate, I would suggest you consider fiberglass frame windows over vinyl frames due to the lower thermal expansion rates of fiberglass as compared to vinyl.

I recently installed Marvin Integrity All-Ultrex fiberglass framed windows in my ICF home. The cost was only marginally higher than builder spec vinyl windows at the lumberyard. The ones I installed have a folding vinyl nailing flange (keeps the nailing flange from getting broken off during handling and installation). We nailed the flanges directly through the exterior foam into the wood backup. The standard frames have a 1" protrusion past the nailing flange. In my case, I will be installing brick with a 1" air gap, so this works out fine. In your case with stucco, I would assume that a traditional 3 coat stucco would extend out from the wall ~1" when completed, so this should work well also. With the Integrity Ultrex windows, you can also order decorative trim that snaps into grooves in the window frame faces if you want a wider frame/trim appearance on the outside.

http://www.integritywindows.com/Ultrex-Fiberglass/