Any of the trims are good but if you want to keep it for a long time I would steer clear of the hybrid systems since they will give you problems as they age. Otherwise, they are great vehicles.

Avoid the hybrids like Mr. Avalance13 said. Also avoid the 2006-2008 Rav4s because those engines cause oil burning. Any trim levels are fine depending on your budget and comfort.

Trim levels, common problems, and reliability would defer by budget and generation, what's your budget?

The 2002-2005 Rav4's are pretty much plastic as I just saw one recently. Everything was so light and extremely low quality. I saw a 2012 rav4 limited and I loved that interior it had a lot of comfort and room. The 2013-2018 rav4's go back to the cappy 2002-2005 Rav4 interiors as they had plastic everywhere and it was just so uncomfortable. If you get a Rav4 in the limited trim, the interiors are going to be a world of a difference in quality. 

Reliability:

2002-2005 Rav4: decently reliable engines, bad tranny's on the 2001-2003

2006-2008 Rav4: awful engines with the 4 cylinder and there were an extreme number of complaints for them. This was the hyundai quality of Rav4's

2009-2012 mid cycle refresh: I highly reccomend this generation as all of the bugs were sorted out and I reccomend any engine, but I like the v6 personally because of the acceleration. Lots of wind noise, as you can expect with rav4's anyway. 

2013-2018 rav4: very reliable and can last a really long time

Overall, I would reccomend the 2009-2012 toyota Rav4 because of the power, reliability, efficiency, nice interior, and looks. 

I bought a 2012 Rav4 yesterday, one owner 138k, paid $11,300 after my mechanic checked it out. 

Personally, I don’t like how the 2012 limited handles. It doesn’t hold the road or do well on gravel like my 2005 RAV Sport sis.