A portable telescope is one that gets used, and that is not a slogan: the instrument that goes outside in one trip on a Tuesday shows more over a year than a larger one that needs planning. The trade is aperture, and it is worth making deliberately.
What portable actually means
Not weight alone. It means the number of trips from the house, the number of parts to assemble, and whether it needs an alignment routine before it works. A 130mm tabletop dobsonian and a crate is one trip and no setup; a 150mm on an equatorial mount is two trips and a polar alignment, and the second gets used far less.
What you give up
Light. A 130mm gathers about half of what a 200mm does, so faint galaxies that show structure in the larger instrument stay smudges in the smaller. On the moon and the planets the difference is much smaller, because those are bright and limited by the air rather than by aperture.
The configurations that travel well
Tabletop dobsonians, short refractors on light alt-azimuth mounts, and small catadioptrics, which fold a long focal length into a short tube. Collapsible dobsonians extend the idea upward: 200mm of aperture that packs into a boot, at a premium over the solid tube version.
Being honest about your own habits
The useful question is not which instrument is best but how often you will carry each one outside. Most people know the answer and buy the larger one anyway. The printed prices in this index put a capable portable instrument at $305.00 and the smallest at $79.95, and both get used more than a heavier telescope does.
Questions people ask about telescope
What is the best portable telescope?
A tabletop dobsonian for aperture per trip, or a small refractor or maksutov if it must fit in a bag. All three are one-trip instruments.
Is a portable telescope worth it?
If it means observing on evenings you would otherwise skip, yes, and that is usually most evenings.
How much aperture do I lose going portable?
Typically one step, so 130mm instead of 200mm. That is significant on faint objects and slight on the moon and planets.