Much depends on context. I would find two dotted quarters a bit confusing. The problem is that the underlying pulse is in three but the notation implies two beats. There are two good solutions. First as already suggested, a dotted quarter followed by an eighth tied to a quarter (or a quarter tied to an eighth followed by an eighth tied to a quarter.) The second would be to use a duplet (of quarters probably).
Generally one doesn't want to break the underlying pulse with dotted notes; tied notes indicate the same rhythm but keep the pulse intact. This is important for those not familiar with the music and trying to read it. The appearance of two dotted quarters may give the impression that the underlying pulse has changed to a duple (6/8) rhythm. Compare with the song "America" from "West Side Story" which alternates pulses of three quarters with two dotted quarters.
For the same reason, the common pattern of dividing 4/4 time into eighths grouped as 3+3+2 is usually written as dotted-quarter + eighth-tied-to-quarter + quarter rather than two dotted quarters followed by an eighth. One point is that rhythmic patterns may vary over a constant pulse.
A personal example is in one piece I had written a bass using a 3+3+2 division of a measure with a treble divided as 1+2+2+1+2 (eighth, quarter, quarter, eighth, quarter). I found it easier to write the bass as dotted-quarter + eighth-tied-to-quarter + quarter and the treble as eighth, quarter, eighth-tied-to-eighth, eighth, quarter than using all dotted quarters in the bass and not splitting the quarter in the treble. Other voices had an essentially 4/4 rhythm.