Iffy call for many folks, especially those who are really just looking to improve their cosmetic appearance. Vital for PLs, OL, throwers and those concerned with performance.
One one hand, low rep, myofibrillar hypertrophy is what's going to make you strongest. On the other hand, sarcoplasmic hypertrophy is generally needed to bring the cross section of the muscle up and to indirectly improve the myofibril's performance.
CONTRARY to popular opinion, sarcoplasmic hypertrophy ISN'T all show and no go.
Let's just go cheap and to Wikipedia:
The Sarcoplasm of a muscle fiber is comparable to the cytoplasm of other cells, but it houses unusually large amounts of glycosomes (granules of stored glycogen) and significant amounts of myoglobin, an oxygen binding protein.
So, sarcoplasmic hypertrophy doesn't offer any DIRECT increases in contractile strength, because you are basically just increasing the fuel and the oxygen-binding capacity of the cell, but, as you can infer, from the direction I'm going, that's not a horrible thing, especially for those borderline strength-endurance efforts that require a bit more glycogen to burn through.
It does, probably, also offer some, in-determinant amount of improved leverage to the myofibrils due to increased cross-sectional area.
There's a reason you see both kinds of hypertrophy.
Let's not forget the valuable effect of high repetitions on the neovascularization of the tissue, either.