I assume you mean OE LSx or Dart SBC.
If you are keeping the power level within the range of an LSx block then LSx it is.
If you are planning on a high end MPH patch then Dart SBC, as it is stronger than an OE LSx block.
If your going with an after market LSx I'll have to defer as it now comes down to total build dollars.

 

Dart LS NEXT SHP PRO takes my vote over the LSX 6 bolt blocks. Way better oiling system and engine builders are going that direction.

 

As GM focuses more on the 3rd version LT1 the LSx parts and availability will drop off. It's great if you want to chase a clearance deal, but bad if you want to see new parts and development. The fully dressed LSx 454 setup that was clearanced was a great deal for anyone wanting that setup.

The Dart block is still new so parts and availability are going to increase over the next few years. That's great if you want to stay current and like getting new parts every so often. The downside is that you won't be catching many sales so it may take a bigger checkbook if you can't time your purchases around the big sales events.

 

 

I vote Dart. It's a better designed block IMO and dart seems to have more deck height options available for you.

 

If you want a really bad *** block get the Dart LSNext 2. It comes with 1/2 inch head and main studs and uses a larger journaled crank with billet caps and comes with a .904 lifter bores. Pretty much bullet proof block wise. Dart has a much better all the way around design imo. The myth that the Dart costs more is bull once all is said and done.