I haven't kept up with the progress of LA's l/h fleet conversion, so I have the following question:

Given a choice between LP's 763 or IB's 346, which would you choose for best seat/travel experience?

This is an award booking (for vacation), so I'm not concerned with variables such as price or timings.

Thanks.

I would go with LP for sure. LP's B763 fleet is relatively young and LAN's in-flight service is superior IB's ancient Business product. Here is a link where you can find more information on Premium Business; which is available on ALL of LAN's long-haul fleet:
http://www.lan.com/en_us/sitio_perso..._business.html

Yeah, but given your username, I'd say there's a chance that you might be a little biased.   

But seriously, thanks for the info -- and for making my decision easier.  I was (unnecessarily) worried that LA might not extend the J upgrade program to include LP metal.

Have IB not converted all their A340 J seating into flat beds now?

Believe so that been said both flat beds
I guess it comes down to crew I would go with LAN Peru as they are quite good crews,
then it comes down better terminal experience in MAD I would assume Iberia to win here?

Plane I would think A346 would be better as further from the engines and the novelty factor for there are not a lot of operators of this type

So in summary if you have not been on LAN go with them if you have then go with IB for a different experience

Avoid Iberia at any cost: their onboard service is not awful (flat bed, good food and wines) but not very good either. But almost all there are the most unreliable people on earth (I had tons on issues with them trying to exchange a ticket, just a date change on an exchangeable ticket... They act randomly and don't care about making you miss the commitments you had in a city, that they actually did). They won't care whether you have a cheap or expensive ticket, or about your FFP status (I have a Gold/Emerald BA card).
On the opposite, LAN people are highly professional, committed and reliable. It is one of the best biz class I've seen (as good or better than Cathay, BA or Swiss for me). They have flat beds and caring staff.
A no-brainer.