The LRP spec 3 was my first big block only my second nitro engine and I didnt find it hard to tune at all.
ORIGINAL: SAVAGEJIM
The Axial will be easier to tune primarily because of its simple sleeve port configuration and its conservative port timings. The D30M and the LRP have more aggressive timings which can be a heartache for tuning if you do not know what you are doing.
For me, the D28M and D30M are easy to tune. I modded my D30M but kept the stock timing profile nd break-in was not a problem at all for me.
Some will say the D30M carburator has some problems due to cheaper quality control protocols, but if you are unfortunate to get a bum D30M/D28M carb, try contacting the seller for an exchange. Most sellers (Racernine and STS Microengines for example) have great service.