racketboy wrote:What's the best way to upscale this for a more modern TV?
This is one of those times when best and cheapest are on opposite ends.
If you're using an external scaler, you're NOT using RF. That'd be like going to a fancy Italian restaurant and asking where SpaghettiOs are on the menu.
Best way is to mod the console to output a better AV signal than RF then use a decent upscaler like an XRGB. RF from an Atari into an HDTV is gonna look like pooh, and the Atari only outputs RF, so the only option is to mod. For the DIYer, a simple composite video mod can be very cheap. There's a ton of different version of composite and S-Video Atari mods on the net, most of them are very cheap to do. This RGB mod (which will also get you composite and S-Video) is about $50 USD, but that's really not a lot compared to some other AV mods.
http://retrorgb.com/atari.html
Of course, if you can't do the mods yourself, you'll have to pay someone to do it for you. But I couldn't imagine someone charging a whole lot for a simple composite mod, so I would go that route if you're light on funds. It'll at least be loads better than RF. S-Video or RGB would be best though.
If you're after better video quality for retro consoles on HDTVs, you might consider getting something like the XRGB Framemeister anyway. It'll make ALL your retro consoles look better on an HDTV, not just the Atari. That has to be considered in the cost of it.
Depending on how attached you are to the Atari, some kind of emulation like RetroPi would be a lot easier and cheaper. Of course, I completely understand the desire to use real hardware, but I just wanted to point that out.
