Sealed bearings have held up a lot better for me, and not just with quads but on aircraft too.
The unsealed bearings with rubber/felt washers (if you're lucky) or steel dust caps seem to get dirty and fail much faster.
They last longer if you service them frequently, but a sealed bearing will last longer still without any maintenance at all.
If it starts getting worn or the seal breaks down, replace.

Not sure if anyone sells a sealed bearing for the cushion lever labeled as such, but if you take your bearing and/or measurements to a bearing shop they'll likely have a sealed Timken bearing that'll fit.
Timken bearings are also held to such high standards that they're acceptable for use off the shelf in aircraft applications, which is saying a lot about their consistent manufacturing.