[SmellyGeekBoy]

I recently purchased a RetroTINK-2X, which is an inexpensive FPGA-based line doubler. It works on a line-by-line basis (as opposed to frame-by-frame like most upscalers) and so lag is virtually nonexistent. I don't have any experience of the more expensive setups like the OSSC or XRGB but it works great for my old consoles.

That said, I still generally prefer to use my PVM CRT monitor for gaming for reasons already discussed in this thread. It really can't be beaten.