seeking a viewfinder


I'm looking for a right angle viewfinder for my EOS350D.
I don't have any experience in optical instruments.

Basically, I'm interested by three types.
I won't consider the 1x-3.3x models, at least not in the the low price
range. 2.5X looks to be enough.
Concerning the construction, the sellers offer three different
9 elements in 8 groups,
9 elements in 5 groups or
10 elements in 5 groups.

What would be the best combination ? What other parameters shall I look for

Thanks in advance and best regards