Direct Play - Player recommendation?

Hoping someone can advise; not the most technical but trying to learn - please be gentle LOL
So converted a nice little PC into my HTPC; stores all my movies. Have it hard-wired to both my router and Samsung TV. I am not sure of now the best way to play my movies?
I run my PMS from my TV through a browser but get regular buffering/server not fast enough headaches - should I instead be using an ie: Roku as a player instead?
My Samsung APP always is saying I am not logged in so gives me headaches - gave up on that.
Thanks if someone could provide some guidance!

Is your HTPC connected to the TV for video?
Then you can use Plex Media Player to have a Plex player on the PC and play video through that. You need to have a keyboard or some sort of remote to navigate through it.
If you want another device to use as a client then a Roku is a good choice. It is probably the easiest setup wise and may be the easiest to use.
What are the specs on your HTPC? You need to be cognizant of transcoding incompatible files unless they are in a format natively supported by the device you are using. A PC supports the most (all?). Other devices support a variety of files, none of them support all (AFAIK).
Take a look at this thread: http://forums.plex.tv/discussion/227370/best-client-for-plex-on-tv#latest

(P.S. What do you mean by

Have it hard-wired to both my router and Samsung TV.

You have a network cable connected from your HTPC to your Samsing?

Thanks for your reply;
I connect my HTPC to my router via CAT6 cable; and then HDMI output to my TV. My TV is connected to my router also with CAT6.
To play, I have been merely selecting that HDMI input on the TV (using a wireless keyboard) and launching my PMS and playing.

My HTPC is as follows:
ASUS Z170M-Plus Motherboard
Intel Core i5 6500
16 GB RAM
Running WIN10

I ask re the ROKU as I run one from my bedroom - doesn’t seem to have the issues?

I used to use a Roku in my bedroom and had no issues at all with it, it ran wireless. Now my wireless network is pretty good, I run a different firmware and I overclock the WiFi.
The Roku is a pretty rock solid device. The 3 is pretty good, the 2 may be a little slow, the Roku
You could run the Windows 10 app or Plex Media Player instead of using the web interface to play. I do not use Windows for anything except work so I am not sure what is the best.

Thanks - will try the PMP and report back! Appreciate the input;-)