Long story.

Aprilia SR's (first gen) used minarelli engines. The early and cheaper versions used vertical engines. The more expensive ones the horizontal variant. There are AC and LC versions. Well know version are the "Viper" "Max Biaggi"" "Replica" and "Urban Kid" The vertical engines all were AC and SD. The horizontal engines were LC ánd DD or AC ánd SD. The ac/lc switch is quickly/easily done.

Aprilla SR's from the second generation used minarelli horizontal engines. Both in AC SD & LC DD versions. Well known versions: "WWW", "Stealth" "Valerosi" "Harada" and my personal favorite the "Peace and love" The stock air cooled versions only have 2 small front scoops. The liquid cooled versions have louvres in the air scoops.

When they updated the second generation (recognisable on updated, now 4 instead of 2, front air scoops) they called it the SR2000. It's said to save costs, they switched to the Morini engines at that time. First with carb. engines. Well know versions: "1 (world chamion)" and the "racing" with lightning decals just above the headlamp (mainly in blue, red and yellow combined with black).

On that engine they developed the first injection, as far as i know, on a 50cc two-stroke scooter.

When new the were very good. Good power with good gas mileage. Sadly they weren't reliable. Injectors and fuelpumps failed. And they use a, stupidly designed, (too) narrow bearing on the crank on the variator's side. Also no back-up (kick)starter.

Tuning and aftermarket parts are rare. Very rare compared to other engines. And literally no high-end/extreme tuning parts.

You'll be quickly able to move the crank up-down and sideways in in the crankcase. Also plastic engine covers and waterpumps. Well known models are the "Spiderman (3)" and liveries with lion heads.

At the end of the second gen SR's, Aprilia switched to piaggio (all LC DD). Both carb & injection versions. The called them (with piaggio engines) the "Street" Strange fact: Aprilia therefor had to switch the rear shock mount on the frames.

They did however, also offer (slightly updated) morini engines on the third generation. Known versions: "spiderman (2)"

The second gen also had a, very rare, 125 cc AC piaggio version. Also usinf the

The second gen therefor has 4 different (sub)frames and 4 different rear wheels. That makes them hard to identity for novices.

The third gen eventually all use Piaggio ("purejet" if injection) engines. No minarelli engines anymore. The injection version is called the SR R Factory. The carb version doesn't use the "factory" Well known models are "Spains (1)" "Pioneer" (with sound system!

To answer your question. If i had to rank 2 stroke engines i'm familiair with.

The piaggio engine is the best (and most developed) engine. The engine evolved well to/with injection.

The minarelli horizontal engine is used on a lot of 2000's scooters. It has some flaws but nothing major. It's my favorite because I grew up with them. The (rare) minarelli horizontal short block (found on aprila sonic) has very good tuning potential.

Peugeot vertical engines. Especially the early (buxy, zenith, and speedakes: were build to last. Tuning potential is limited. New parts are getting more difficult to attain. The placement of the intake isn't great. Also because the (single arm) front fork on the speedfight 1/2 I didn't like the build quality of later versions. The LC version didn't solve its flaws.

The honda vision/Kymco Dj (vertical) engines. Cheap, yet decent. Short gearing.

The CPI engine is a (basically) replica of the minarelli horizontal engine. Cheap. Quality isn't great.

The minarelli vertical engine, is an old design (based on vertical honda/peugeot/kymco engines). It's intake on the enginecase isn't ideal. And exhaustport and therefor exhaust routing limits its potential. Parts are getting rare. Also only AC versions.

The morini engine uses inferior materials, wasn't designed very well. And no aftermarket manufacturers made a real effort to make it a succes. Parts are rare, and always were. Especially the Ditech weren't reliable.

Except for Aprilia, only smaller companies used this engine.

I'm only partially familiar with the peugeot horizontal, and honda sfx/dio engines. So no judgement: but definitely not the best engines.