As much as I love the elite-upside and potential of a guy like Markstrom, I would still take Mike Smith for a couple reasons.
As Pengwin said, Mike Smith is the proven entity and he's playing in a very favorable defensive system right now.
Next, the thing about Markstrom is that he is still a "dynamic entity" (as Justin Goldman would say), thus he will have quite a challenge adapting to the NHL once its shooters have learned his tendencies and adjusted to him. Once he is no longer a dynamic entity, anything is possible (see: Mason, Steve).
Smitty is the guy for me.
MounD - Double Threat FHL (18-19 champs)
10-Team Yahoo daily H2H Dynasty
3C, 3LW, 3RW, 6D, 2G, 7Bn (IR)
G, A, +/-, PPP, SHP, SOG, FW, HIT, BLK // W, Sv, GAA, Sv%, SHO
C: Bergeron, Barkov, Aho, Point, Kadri
LW: Marchand, Landeskog, Hertl, Marchessault
RW: Stamkos, Tarasenko, Laine, Palmieri
D: Carlson, Letang, Dumba, Weber, Pietrangelo, Ristolainen, Byfuglien*
G: Bobrovsky, Holtby, Lehner, Greiss-Varlamov
Farm: Turcotte, Cozens, Denisenko, Newhook // Sandin, Jokiharju, Dobson, K'Andre // Shesterkin