The Catch-Up entry is the most basic version of uchimata entry and is very common. It is the technique used by great uchimata men like Neil Adams (GBR).
The Back-Step entry is perhaps easier for beginners to learn as there is less balancing required compared to the Catch-Up entry.
The Hop-In uchimata is very popular at international competitions too. Ryunosuke Haga (JPN) and Rafaela Silva (BRA) both use this entry for their uchimata.
The Pivot entry was popularized by American judoka and coach Hayward Nishioka. It is the precursor to the spinning uchimata. Actually, Nishioka refers to his pivot uchimata as "spinning uchimata" but the spinning uchimata popular in Europe involves an additional action of whirling uke around first before doing the pivot. So the Pivot entry is actually preparation for the Spinning entry.