The main advantage of the value plan lineup is the truly unlimited data offering, which you can't get with the Monthly 4G plans (they are "unlimited" with throttling after a few GB, and trust me, you don't want to know how bad the throttled speed is). You can get 500 voice minutes and unlimited data for $55/mo, and though tethering isn't allowed they can't really stop you if your phone is unlocked. No other carrier offers anything remotely similar.
If you don't want to tether, though, Monthly 4G is definitely the way to go. $30/mo for 100 minutes and 5 GB data; all you need is a VoIP app and that's perfectly serviceable, and again no other carrier offers anything similar.
T-Mobile will block you if you tether on Monthly4G. Your phone data will still work, but if you use it for more than a couple minutes, the tethering will start going to dead links.
T-Mobile's tethering block works like this: They sniff your unencrypted HTTP traffic for user agents that look like they came from a Windows machine, and if they find one they hijack the connection and redirect you to their tethering upsell page. They can't sniff HTTPS connections, so HTTPS continues to work. For HTTP you can change your user agent, or just use a Mac (which their sniffer isn't smart enough to detect, yet).
If their sniffer becomes smarter in the future you can always switch to a VPN for your tethering traffic, which they wouldn't be able to distinguish from a VPN connection made by the phone itself.
Ultimately, as long as you have full control over your phone they can't stop you from doing what you like with the data you're paying for. Of course, I wouldn't recommend relying on routine tethering without paying your carrier for it, but it's really nice to have on occasion.
This has not been my experience. I have never been sent to dead links.
I have had them try to send me to a "mobile hotspot feature" upsell page when using Chrome from my laptop while tethering. I figured out that they were checking browser user-agents to determine whether a user was tethering or not.
But the Chrome app on Android allows changing the user-agent to the desktop equivalent with its "request desktop site" feature. So I called and yelled at them saying that they had no right to block me from using my phone in the way that I wanted. They flipped a bit somewhere and I haven't had a problem since.
If you don't want to tether, though, Monthly 4G is definitely the way to go. $30/mo for 100 minutes and 5 GB data; all you need is a VoIP app and that's perfectly serviceable, and again no other carrier offers anything similar.