I have experience with Chromecast and Roku.
CHROMECAST: Chromecast not only requires a phone, tablet, or laptop (to set it up), but an INTERNET CONNECTION! No internet? No Chromecast. So unless you have an internet connection where you camp, Chromecast will not be a good choice. So the big problem is that a Chromecast requires an internet connect to function as a LOCAL STREAMING DEVICE.
ROKU: We have a ROKU HD, ROKU 1, ROKU Stick and a ROKU XS HD (think we like them?) Hands down, ROKU has more apps and channels that *ANY* other streaming solution. Unlike Chromecast, the ROKU products do not require an internet connection to function as a LOCAL STREAMING DEVICE.
Wait! What is a LOCAL STREAMING DEVICE and what are my options, you ask?
A LOCAL STREAMING DEVICE is a means of streaming content that you have on your laptop, phone, hard drive, DVR etc.
Options? LOTS! Fart too many to cover them all here, but probably the most popular are:
LAPTOP / PC: Windows Media Center or PLEX, and there are many more.
PHONE: pretty much any content you have.
TABLET: pretty much any content you have.
HARD DRIVE: Depending on the technology supporting it and whether or not you have a router, pretty much any content you have.
We use PLEX Media Server. Here's why:
MEDIA: Photos, home movies, moives (DVD collection or???), Music (CD's or ???) and streaming channels. (wait, streaming channels? Yes, PLEX has literally 100 of them)
REQUIREMENTS: Windows, MAC or LINUX Computer (for server), ROUTER (for local network, but more functions with internet connected router) and CLIENT (ROKU, some smart TV's, Android and Apple phones and tablets and more)
SIMPLICITY: Easy to install, excellent (community) support.
EASE OF USE: As easy as any other quality streaming solution.
Did I mention that PLEX is free?
Anyway... So here is what we have in the RV:
2 TV's (42" smart in Living room and 32' not so smart in bedroom)
DirecTV HD DRV (in living room, from home), SL3 dish (takes about 10 - 20 minutes to setup) and Genie client (for bedroom)
ROKU XS HD (in living room) and ROKU Stick (in bedroom)
Wireless router, with repeater capability (provides secure, local "coach network" and can connect to internet from RV park or any of our other 3 sources, T-Mobile, AT&T and Verizon.
Laptop (actually 3, and 3 tablets and 3 phones) with PLEX Media server and over 400 movies, bunches of home videos, thousands of songs and thousands of photos, all can be streamed to the TV's, other laptops, tablets, phones or... even guests and nearby RV's if we want (via a secured guest network).
Home is where we park it.