Have owned both. Still own SMv and it may never leave. TWD is a very good pin. SMv is a great pin.
For me, TWD had way too many shots that end in the useless pop bumpers, and the code relies way too much on the drop targets. Drops should have been used for either mode light or blood bath...not both. Felt like that was 75% of what I was ever shooting for. Other than that...amazing game. Those two things kept it from being a keeper for me though. That said, I would never say never for owning one again someday.
SM is one of my favorite games ever. The shots are all super satisfying and the code is fun. Nowhere near as deep as TWD, but it works perfectly with the layout. Owned a red, loved it but wanted a mint condition one. Sold it once the vault came out and was able to land one of those a few months ago. I love both forms...slightly prefer the vault, but the original as awesome too.