It all depends on what you're looking for in terms of how advanced it should be, how high maintenance you want it to be, how large, whether you want the screen to be in colour, etc.
- The vintages are small and very simple in comparison to the ones you have now, with a sort of cute theme for each one released after the original p1 and p2. They vary in maintenance level required, look them up individually for example
here.
- The connection series are similar in size and graphics to your entama, but in english.
v1-v3 are simpler, with v1 being the very simplest. v2-v3 have a LOT of characters. They are all gender neutral and seem to have no structured growth pattern or way to predict what character you're gonna get, which is either fun, cute and refreshing or irritating depending on how you want to look at it. Games and items are plentiful and just fine. v3 has two more games, but v2 gives a more vintage-y feeling
Average to low maintenance.
v4-v4.5 would be the standard connections. They are the most reliable in predicting what character you will get, thanks to the skill point system. They have fun games, a good amount of characters, go to school and get a job with a minigame as adults. Average maintenance.
v5 and v5.5 are family-themed tamagotchis, where you care for up to three at once. Apart from the family-themed character set, they are rather simple and low maintenance. Wide screen, like the tama-go, but no grayscale.
v6 is the Music Star. A really fun pet in which the aim is to make your tamagotchi a first-ranked rock star, but high maintenance. Wide screen, like the tama-go, but no grayscale.
- The color tamagotchis are quite a lot bigger than the connections, yet smaller than the tama-go. They feature lcd-screens in colour, more modern and humanoid characters, and a sort of progressive gameplay where you earn more locations for your tama to go to the further you progress with the generations. Medium to low maintenance for the different versions. All are in japanese though, with few exceptions. The ID L came out in english in a special Hong Kong release, but they're really hard to catch hold of by now and pretty expensive. Best shot for an english colour tama is probably the p's. There is an english patch for the tamagotchi p's on the internet, that you download via infrared using a phone with IR or an IR-usb device. Friendly tamatalkers will help you with this if you decide to catch hold of a p's. They are rather low maintenance and have lots of fun features, downloadable items and games, but the characters are mostly girly-humanoid-modern.
- Most of the special releases are in japanese, so I won't mention them here. One fun and quirky special tamagotchi is in english though - the tamawalkie. A pedometer pet that features a tamagotchi (you choose one out of three at the startup) traveling around USA to fix his/her broken spaceship and collect souvenirs. It requires a lot of walking or shaking, but is cute and fun with nice minigames otherwise. A good choice if you like walking and want a tamagotchi that's... not ordinary
If any of these tamas caught your interest - google them for more in-depth descriptions. There are also really good youtube reviews on almost all versions. Personally, I'd probably recommend a connection. Though a bit older now, you can still find them online for good prices. They're in english, have a good size, and a good amount of features and cute characters for one who wants to get back into tamagotchi. v1 if you like simple, music star if you like a challenge. v2-v4.5 for something in between.
Good luck!