Operators face upgrade dilemma: HSPA+ or LTE?

I dont think there is any dilemma at all. There is no confusion at all for the 3GPP (3G/HSPA) based operator on this aspect. Look at the Europe and asia. Eveybody is gonig forward with HSPA+. Its gonig to be natural migration to LTE for them when time is right. And that means four to 5 years from now.
This dilemma is only created due to the hype of the CDMA based operator going to the LTE for data. So, even in this case AT&T is clear about its own HSPA+ plan..eventhough Verizon is going with LTE.
So, CDMA based operator migrating to LTE is its own choice ...as they cannot go to the HSPA+..
I think every operator are quite capable to make a judgement in this case.

couldn't have said it better. GSM operators will and should milk their existing investments until it's time to move to LTE.

Agreed totally. In 3gpp standards, no surprise: operators do not need to think: they just have to follow release after release.

I think the Standardisation bodies also must try to have a very clear cut migration path defined in the standards written , otherwise every Operator tries to experiment its own way of going ahead on Network Technology Upgrade. For eg- in LTE case specially with Verizon announcing migration to LTE there has crept this confusion of whether one goes through the progression paths or directly to LTE. But I fully endorse that operators must follow releases as in the order they come as this is the best way to fully utilise existing infrstaructure & also it does not put pressure on the Vendors to invest too much of time in designing non standard migrations

one thing that most industry seems to ignore is the fact that many 3G operators are really struggling today with capacity in dense areas and have to do what is called cell site splitting to be able to support the data explosion they are seeing today. Doing so and upgrading all the associated backhaul and core networks is extremely costy + operators have to find new sites in extremely congested areas, rebuild and install sites, purchase ancillaries...
Adding LTE to an existing site is a much more cost effective proposition as it is a fraction of the cost of a brand new site and adds 3-4x time the capacity of HSPA+ even in 5MHz channel (if you look pass the the headline peak rate and the true capacity benefit LTE brings compared to HSPA/HSPA+)...
You just need to look at why the nordics operators are so keen to go LTE as fast as poasible; with average sub data consumption over 1GB/month the business case for LTE is pretty clear compared to pouring money into legacy technology that only provides a stop gap to LTE.

to the first comment - so if 4-5 years is the right time for LTE migration for GSM operators what will happen to CDMA operators. No HSPA+ and no LTE??!