-Starting with Power Rangers: Lost In Space, team-ups with past Power Rangers became a tradition. Some were morphenomenal while others were so bad they'd give Rita a headache.
-Watchmojo has counted down 10 team-ups, 5 that were the best and 5 that were the worst.
Worst
5. Power Rangers Time Force: Time For Lightspeed
-Would've worked better as a 2-parter
-The villain was generic
-Vypras return was never fully explored.
4. Power Rangers Operation Overdrive: Once A Ranger
-Overdrive Rangers give up to easily.
-Rita/Zedd have a son who is a weak villain
-Was a weak 15th anniversary teamup
Best
3. Power Rangers Wild Force: Reinforcements from the Future
-Jen is badass
-One of the best team up fights
-Ransik gets redemption
-Both series see their stories advance
2. Power Rangers Lost Galaxy: To the Tenth Power/Power of Pink
-Return of the Psycho Rangers
-Kendrix, Pink Galaxy Ranger dies in the line of the battle
-The first true team up episode of Power Rangers
Fun Fact: Cassie, Pink Space Ranger was going to leave the In Space team and take up Kendrix's mantle as Pink Galaxy Ranger but a pay dispute caused the actress to leave even though she had filmed a couple of scenes. They quickly scrambled to bring in Karone who was formerly known as Astronema "Princess of Evil" in PRIS.
Source
I pray that since Hasbro taken over that they put some effort and $$ back into the team ups.